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Cite This: J. Phys. Chem. C XXXX, XXX, XXX−XXX

Adsorption and Reaction Pathways of 1H‑1,2,3-Triazole on Cu(100) and O/Cu(100) Shang-Wei Chen, You-Jyun Chen, Yun-Hsien Chen, Guan-Jie Chen, Sheng-Hsun Chan, and Jong-Liang Lin* Department of Chemistry, National Cheng Kung University, 1 Ta Hsueh Road, Tainan 701, Taiwan, Republic of China

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S Supporting Information *

ABSTRACT: The adsorption and reactions of 1H-1,2,3-triazole on Cu(100) and oxygen-precovered Cu(100) [O/Cu(100)] have been investigated using the combinative techniques of temperature-programmed reaction/desorption, X-ray photoelectron spectroscopy, reflection−absorption infrared spectroscopy, and near-edge X-ray absorption fine structure in addition to density functional theory calculations. Although the 1,2,3triazole molecules may have 2H-tautomeric form, it is found that the 1H-form is predominantly adsorbed on Cu(100) at 120 K. The adsorbed 1H-1,2,3-triazole molecules interact with each other via hydrogen bonding. The triazole molecules on Cu(100) undergo N−H bond scission first to form nearly perpendicular 1,2,3-triazolate on the surface. H2 evolves below 350 K through two different mechanisms depending on the coverage. The triazolate on Cu(100) further decomposes to form H2, HCN, N2, and CH3CN at ∼550 K. The latter three products are generated by the triazole ring opening with preferential bond dissociation steps. On O/Cu(100), the triazole molecules deprotonate first by N−H breakage, forming H2O at ∼200 K but without H2 desorption below 350 K. The 1,2,3-triazolate reacts to generate H2, N2, H2O, CO, and CO2 at a lower temperature of ∼465 K in the presence of surface oxygen. C−CN and/or CCN containing intermediates are likely to be formed on the surface from the triazole ring rupture and are suggested to be responsible for the formation of 1H-azirine or vinylideneamine.

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INTRODUCTION Triazole molecules contain a five-membered ring of three nitrogen atoms and two carbon atoms and have been immensely used in biological activities as antifungal drugs and plant protection fungicides.1 1,2,3-Triazoles can be synthesized, via a click chemistry method, by the reactions between azides (−N3) and alkynes. Recently, copper [Cu(I)]catalyzed azide−alkyne cycloaddition reactions to form triazoles have obtained broad interest because of the mild conditions, high yields, and greater tolerance of functional groups and have found a variety of applications in biomolecular ligation, polymerization, surface modification, and preparation of functional materials.2 Because of the distinguished role in metal coordination, a number of conjugated triazole-containing molecules or polymers have been reported to be optical sensors of metal ions.3 Coordination of the metal ions with the triazole ring can change the emission efficiency of fluorophore systems.4 The 2N and 3N atoms of the 1,2,3-triazole ring are the active sites binding to metal ions including Cu+ and Cu2+.5−8 The two nitrogen atoms can coordinate individually or simultaneously, as illustrated in Scheme S1. In this paragraph, surface applications regarding using triazoles are described. 1H-1,2,3-Triazole has been used as a precursor to prepare hydrogenated carbon-nitride films by © XXXX American Chemical Society

plasma-enhanced chemical vapor deposition and tested as a corrosion inhibitor of copper in NaCl solutions.9,10 The protective layer is suggested to be a polymeric network formed by the dehydrogenated triazole molecules and copper ions.10 The click chemistry of azide−alkyne cycloaddition has been applied to form triazole-containing adhesive polymers for copper plates.11 It is believed that the reaction is catalyzed by Cu+ generated from the surfaces of the copper plates. Moreover, the click method can be used to prepare 1,2,3triazole-containing self-assembled monolayers (SAMs) on gold and silicon surfaces.12−15 On Au, the first step is to modify the surfaces with thiolate SAMs possessing azido terminal groups [−S(CH2)nN3], which further react with alkynes (HCC−X) in the presence of Cu(I) to form 1,2,3-triazoles. The chemical structures of the X groups, such as ferrocene or aromatic moieties, become a key part in tailoring the surface properties.12,13 On Si, alkyne-terminated monolayers (Si− CHCH−(CH2)n−CCH) are first prepared, instead, by hydrosilylation of a dialkyne species (HCC−(CH2)n−C CH), followed by the cycloaddition reaction with azides (Y− Received: August 17, 2018 Revised: October 12, 2018 Published: November 8, 2018 A

DOI: 10.1021/acs.jpcc.8b08007 J. Phys. Chem. C XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry C N3).14,15 In this case, the Y groups can change the surface functionalities.14,15 Other than the SAMs on Au and Si surfaces, 1,2,3-triazoles have been directly chemically attached to a H-terminated carbon surface, prepared by the reaction with IN3 in the gas phase to form surface-bound N3 groups and by the subsequent reaction with alkynes (HCC−R).16 Interestingly, the cycloaddition between 4-azidobiphenyl and 9-ethynylphenanthrene has been suggested to occur directly on Cu(111) at room temperature in an ultrahigh vacuum without using a solvent and Cu(I), from the study using scanning tunneling microscopy.17 In the previous reports of 1,2,3-triazole-containing surface species on Si, C, and Cu, their thermal stability and possible reaction pathways have been lacking and unrevealed.10−17 1H1,2,3-Triazole can be used as a model compound for the studies of surface chemistry of triazoles. Previously, thermal decomposition of 1H-1,2,3-triazole was found to generate CH3CN.18−20 However, a theoretical study has suggested multiple possible reaction routes for the dissociation of 1H1,2,3-triazole, including NH or CH hydrogen abstraction and retro-[3 + 2]-cycloaddition reactions.20 For the latter case, HNNN + HCCH, HNNCH + HCN, HNC NH + HCN, and/or HNCCH2 + N2 can be possibly formed. For the products of HN3 and C2H2, they are from a reverse cycloaddition of azide−alkyne, forming 1,2,3-triazole. In the studies of the molecular geometries and rotational and vibrational spectroscopies of 1,2,3-triazole, the possible tautomerism between 1H- and 2H-1,2,3-triazole has been noticed previously.21,22 1H-1,2,3-triazole is reported to be predominant in the gas phase in the earlier papers before 1975.23−25 However the more recent study, with combinative techniques of spectroscopy, electron diffraction, theoretical calculations, and isotope labeling, suggests that 2H-1,2,3triazole is the more abundant species in the gas phase at room temperature.26 Although 2H-triazole may be more stable in the gas state, the 1H form is favored in a polar solvent because of a higher dipole moment.27 In toluene, the 1H nuclear magnetic resonance experiment shows that the 1H tautomer is more favorable at 175 K.28 In the crystal phase, 1H- and 2H-1,2,3triazole form a molecular complex linked by a NH···N hydrogen bond.29 In the previous tautomerism studies of 1H- and 2H-1,2,3-triazole, the tautomeric state of this hydrogenated 1,2,3-triazole on a surface was not included. In the present study of 1H-1,2,3-triazole on Cu(100), we focus on the adsorption state and bonding geometry of this molecule, with a comparison to the cases of 1,2,3-triazole coordination to copper ions, examination of the reaction intermediates and their relating reaction products, and exploration of the effects of preadsorbed oxygen atoms.

in a single desorption experiment, and the Cu(100) surface was positioned ∼1 mm from an aperture (3 mm in diameter) leading to the differentially pumped mass spectrometer. A heating rate of 2 K/s was used. The thermal reaction products of 1H-1,2,3-triazole on Cu(100) were identified in terms of their parent ions or cracking patterns. In the RAIRS study, the spectra were recorded at a grazing incidence angle of 85° through a KBr window. The reflected beam was refocused on a mercury−cadmium−telluride detector. An air scrubber was used to remove CO2 and H2O present in the entire beam path. All infrared (IR) data were accumulated by recording 1000 scans at a 4 cm−1 resolution and ∼115 K. 1H-1,2,3-Triazole (97%), purchased from Sigma-Aldrich, was subjected to several cycles of freeze−pump−thaw before introducing its vapor into the vacuum chamber. X-ray photoelectron spectroscopy (XPS) and near edge Xray absorption fine structure (NEXAFS) experiments were conducted at the National Synchrotron Radiation Research Center of ROC. In the XPS measurements, a photon energy of 620 eV was used, and the photoelectrons were collected at an angle of 50° from the surface normal, with the total instrumental resolution estimated to be better than 0.3 eV. The binding energy was scaled according to the bulk Cu2p3/2 peak at 75.10 eV. Some of the presented XPS spectra were fitted with Gaussian−Lorentzian functions after Shirley background subtraction. Polarization-dependent nitrogen Kedge NEXAFS measurements were performed in terms of the total electron yield (TEY) method. The intense 1s → π* transition of highly oriented pyrolytic graphite at 285.38 eV was used as a reference for the photon energy scale. The X-ray absorptions were first normalized to the photon flux, measured from the current of a freshly evaporated gold mesh positioned in front of the Cu(100) surface, to form a so-called I0normalized spectrum. The presented X-ray absorption spectra of adsorbed species were obtained by dividing the I0normalized TEY spectrum of an adsorbate-covered Cu(100) surface by the I0-normalized TEY spectrum of a clean Cu(100) surface. In the present study, the oxygen-precovered Cu(100) was prepared by exposing the clean surface at 500 K to 30 L O2, and the coverage of oxygen atoms was assumed to be ∼0.2 monolayer.30

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COMPUTATIONAL METHOD In our theoretical cluster model for the optimized bonding geometries of 1H-1,2,3-triazole and triazolate, the Cu(100) surface was represented by two slabs with a total of 41 Cu atoms fixed at their lattice positions. The density functional theory (DFT) calculations were performed using the generalized gradient approximation with Perdew and Wang exchange−correlation functional in the Cerius2-DMol3 package. A double-numeric quality basis set with polarization functional was used for the all-electron calculations including relativistic effect for the core electrons. No scaling factor was used for the calculated frequencies of 1,2,3-triazolate on Cu(100) in this article. The mode assignments for the theoretical frequencies were based on the animated molecular vibrations. The transition state (TS) and the reaction path between two equivalent 1,2,3-triazolate surface species were searched by implementing the program package of Accelrys DMol3 in Materials Studio. The integrated linear synchronous transit/ quadratic synchronous method was used to obtain the preliminary TS, followed by full TS optimization. The

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EXPERIMENTAL SECTION Temperature-programmed reaction/desorption (TPR/D) and reflection−absorption infrared spectroscopy (RAIRS) experiments were conducted in an ultrahigh vacuum chamber (a base pressure of approximately 2 × 10−10 Torr). The Cu(100) single crystal (1 cm in diameter) was cooled with liquid nitrogen and resistively heated to high temperatures. A K-type thermocouple was inserted into a hole on the edge of the crystal for temperature measurement. Prior to each experiment, the surface was cleaned by cycles of Ar+ ion sputtering and annealing until impurities were undetectable by Auger electron spectroscopy. In the TPR/D studies, the quadrupole mass spectrometer was capable of acquiring 20 different masses B


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The Journal of Physical Chemistry C confirmation of the pathway connecting the relevant reactant, TS, and product was achieved using intrinsic reaction path calculations in terms of the nudged elastic band algorithm.

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RESULTS AND DISCUSSION Adsorption of 1H-1,2,3-Triazole on Cu(100). Shown in Figure 1 are the triazole temperature-programmed desorption

Figure 2. TPR/D spectra of 0.05 L of 1H-1,2,3-triazole on Cu(100), showing the evolution of H2, HCN, N2, and CH3CN.

cleavage. On Cu(100), it has been reported that self-coupling of H atoms occurs near 300 K to evolve H2.31 H2 desorbtion at 315 K shown in Figure 2 is consistent with this mechanism. The other three products of HCN, N2, and CH3CN evolving at 565 K are presumably due to rupture of the triazole ring. The high-temperature H2 peak at 580 K is associated with the ringopening process and dehydrogenation. Note that the 175 K peak in the 28 amu trace is due to CO desorption from the background. The coverage-dependent TPR/D spectra of 1H-1,2,3triazole on Cu(100) at 0.05, 0.3, 0.5, 0.7, and 1.0 L are shown in Figure 3. As compared to the 0.05 L case, two different desorption patterns are observed at higher exposures. For H2, the 315 K state is hardly detectable but is shifted to lower temperatures (∼165 K in the 0.3 and 0.5 L cases). This low-temperature H2 formation channel cannot be explained by the atomic H recombination on Cu(100) and should be related to a close molecular packing on the surface at a larger coverage. That is, the H2 formation at 165 K likely originated from the interaction between the adsorbed 1H-1,2,3-triazole molecules. However, the H2 signal is not due to the parent molecule desorption, which is not observed at 165 K, as shown in Figure 1. In addition, the high-temperature H2 peak is shifted to 560 K at higher exposures, and the formation temperatures of the other three products (HCN, N2, and CH3CN) are lowered by ∼5−20 K. The ring opening of 1,2,3triazole occurs at lower temperatures in the high-coverage conditions. Note that no cyanogen [(CN)2] was found as the reaction product of 1H-1,2,3-triazole/Cu(100). Spectroscopic Analysis of 1H-1,2,3-Triazole on Cu(100). XPS. Figure 4 shows the XPS spectra of 1H-1,2,3triazole (0.5 L) on Cu(100) as a function of temperature. For the triazole molecules adsorbed on Cu(100) at 120 K, the C1s emission is fitted with two peaks of 285.6 and 286.6 eV and the N1s emission with three peaks of 400.2, 401.5 and 402.8 eV. In the previous XPS study of 1H-pyrazole, with an amine

Figure 1. TPD spectra, represented by the molecular ion, from 1H1,2,3-triazole adsorbed on Cu(100).

(TPD) spectra, represented by the molecular ion of C2N3H3+. No molecular desorption is found at 0.05 L, indicating that the 1H-1,2,3-triazole molecules completely decompose on Cu(100) at the dosing temperature or in the linear heating process of the TPD experiment. In the 0.1 L spectrum, a small feature is observed at ∼220 K, and it reaches a maximum at 0.5 L. From 0.3 to 0.7 L, a new desorption state appears at ∼200 K. These two states (200 and 220 K) are considered to be from the first-layer adsorption molecules but with slightly different adsorption energies, as they do not grow with increasing exposures. There is an additional 193 K feature in the 1.0 L spectrum. For this state, the peak temperature shifts to 201 K at 3.0 L, also with an enhanced peak intensity. Figure S1 shows the triazole desorption spectra at larger exposures (1.0−3.0 L), showing overlapped leading edges of the desorption traces. With these desorption characteristics, the peaks of 193, 196, and 201 K from 1.0, 1.5, and 3.0 L respectively, are attributed to multilayer desorption. Thermal Reaction of 1H-1,2,3-Triazole on Cu(100). Figure 2 shows the TPR/D spectra of 1H-1,2,3-triazole/ Cu(100) at 0.05 L, with evolution of the reaction products of H2, HCN, N2, and CH3CN. Their formation is confirmed by the molecular ions and/or fragmentation patterns, which are shown in Figure S2 for HCN (m/z 26 and 27), N2 (m/z 14 and 28), and CH3CN (m/z 38, 39, 40, and 41). As shown in Figure 2, the H2 desorption peaks mainly appear at 315 and 580 K, with a 270 K shoulder, indicating that the two main states result from different, reaction-limited H2 formation mechanisms. In terms of the chemical structure of 1H-1,2,3triazole, the hydrogen source relates to C−H or N−H bond C


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The Journal of Physical Chemistry C

Figure 3. TPR/D spectra of 1H-1,2,3-triazole/Cu(100), at 0.05, 0.3, 0.7, and 1.0 L for the reaction products of H2, HCN, N2, and CH3CN.

Figure 4. Temperature-dependent XPS spectra of 0.5 L of 1H-1,2,3-triazole on Cu(100). All of the spectra were measured at ∼120 K. The 1H1,2,3-triazole molecules were adsorbed at ∼120 K, followed by progressively heating the surface to the temperatures indicated.

D


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The Journal of Physical Chemistry C (−NH−, 1N) and an imine (−N, 2N) group, the N1s binding energies for the 1N and 2N have been reported to be 402.4 and 401.2 eV, respectively, with a difference of 1.2 eV.32 For the three carbon atoms in the pyrazole ring, their 1s peaks are located at 285.5, 286.3, and 287.1 eV.32 Our N1s fitting peaks at 401.5 and 402.8 eV in the 120 K spectrum are consistent with those of 1H-pyrazole, from the imine and amine groups, in terms of the two characteristic binding energies and their differential. Besides, the area ratio (∼2:1) of 401.5 eV/402.8 eV further supports the assignments of 401.5 eV to −N and 402.8 eV to −NH− for the molecularly adsorbed 1H-1,2,3-triazole. However, the smaller peak at 400.2 eV in the 120 K spectrum of Figure 4 is attributed to a dissociated 1H-1,2,3-triazole, which becomes a predominant peak at higher temperatures. In terms of the relative areas for the 400.2, 401.5, and 402.8 eV peaks, the Cu(100) surface is mainly covered with the intact 1H-1,2,3-triazole molecules at 120 K. As a reference, for the surface species containing 1,2,3triazole rings generated by azide−alkyne cycloaddition on Cu and Si, the N1s binding energies for−N and −NC− are reported to be in the ranges of 400.2−400.7 and 402.2−402.5 eV, respectively.14,15,17 The C1s fitting peaks at 285.6 and 286.6 eV in the 120 K spectrum can be ascribed to C1s core levels of C−C and/or C−N groups.32 The predominant 286.6 eV is mainly from undissociated, adsorbed 1H-1,2,3-triazole. However, the CO adsorption on Cu(100) from the background, as evidenced by the TPR/D result (Figure 2), may have a contribution to the intensity at ∼286.6 eV. The C1s binding energy of CO on Cu(100) has been reported to be at 286.6 eV.33 Besides, the presence of the smaller 285.6 eV signal can be attributed to a dissociated 1H-1,2,3-triazole on Cu(100). Upon heating the surface to 180 K, the N1s peaks of 1H1,2,3-triazole are shifted to 401.1 and 402.2 eV, still with an area ratio of ∼2:1. These shifts could be due to a variation of the interaction between the adsorbed 1H-1,2,3-triazole molecules and/or a variation of surface bonding sites. In addition to the changes in the N1s binding energy, the total area of 1H-1,2,3-triazole diminishes from 120 to 180 K. As a contrast, the other N1s emission signal of 400.2 eV grows. This result can be realized by dissociation of 1H-1,2,3-triazole and formation of new surface species. Because H2 evolution occurs at ∼165 K in the reaction of 1H-1,2,3-triazole on Cu(100) at 0.5 L, as shown in Figure 3, the enhancement at 400.2 eV upon heating to 180 K can be connected to a dehydrogenation process, especially relating to the −NH group. In the case of C1s, the temperature rise increases the intensity at 285.6 eV at the sacrifice of 286.6 eV. At 350 K, only two peaks are observed, 400.2 eV for N1s and 285.6 eV for C1s. The adsorbed 1H-1,2,3-triazole disappears at this temperature because of its desorption in the range of ∼180−240 K (Figure 1) and further reaction, with evidence of the increased intensities at 400.2 and 285.6 eV from 180 to 350 K. Progressively heating the surface to 480 K leads to the same XPS spectral features for the 1s core levels. Note that the surface intermediate from the thermal dehydrogenation of 1H-1,2,3-triazole is stable prior to ∼500 K, as shown in Figures 2 and 3, and its decomposition produces H2, HCN, N2, and CH3CN at ∼560 K. Interestingly, the three nitrogen atoms and the two carbon atoms of this intermediate are indifferentiable by the 1s XPS spectra, with one emission peak of 400.2 eV for nitrogen and also one peak of 285.6 eV for carbon. In the 620 K spectra of Figure 4, these two C1s and N1s peaks no longer exist, which are consistent with the thermal reaction of the responsible surface intermediate. This

intermediate is suggested to be 1,2,3-triazolate (C2H2N3, i.e., 1,2,3-triazole anion) because it is generated from the hydrogen loss of 1H-1,2,3-triazole, particularly relating to the NH group, and its decomposition by ring-opening can form the C- and/or N-containing products of HCN, N2, and CH3CN. The possible origins for that just one N1s peak is observed from 1,2,3triazolate are discussed later. RAIRS. Figure 5 shows the RAIRS spectra of 1.0 L of 1H1,2,3-triazole on Cu(100) as a function of the surface

Figure 5. Temperature-dependent RAIRS of 1.0 L of 1H-1,2,3triazole on Cu(100). All of the spectra were measured at ∼120 K. The 1,2,3-triazole molecules were adsorbed at ∼120 K, followed by progressively heating the surface to the temperatures indicated. The spectra of 230−610 K have been multiplied by a factor 3.

temperature. Note that the 1.0 L exposure can render multilayer adsorption at 120 K as shown in TPR/D study (Figure 1). In the 120 K spectrum, the absorptions appear at 702, 794, 819, 883, 956, 975, 1078, 1114, 1240, 1421, 1539, 2904, 3020, and 3157 cm−1. These set of peaks are listed in Table 1 and are compared to those of 1H- and 2H-1,2,3triazole, suggested previously by vibrational studies in the liquid state and theoretical calculations.21 First of all, no IR peaks due to N−H stretching absorption are detected in the 120 K spectrum. The N−H stretching peak appears at ∼3500 cm−1 in the previously reported IR spectra of 1H- and 2H1,2,3-triazole in the vapor state but is shifted to ∼3450 cm−1 in CCl4 or CHBr3.23 Moreover, the N−H stretching mode is no longer observable in the triazole liquid state, which is likely due to hydrogen bonding of the triazole molecules.23 This NH···N interaction may also occur between the adsorbed 1H-1,2,3triazole molecules on Cu(100), resulting in the missing N−H absorption in the range of ∼3350−3500 cm−1 in the 120 K spectrum of Figure 5. In addition, the broad absorptions at 2904, 3020, and 3157 cm−1 in the 120 K spectrum could be assigned to C−H stretching modes, Fermi-resonance of the N−H modes, overtones, or combinations.23 On comparison of the 120 K spectrum to the previously assigned peaks of 1Hand 2H-1,2,3-triazole (Table 1), it is found that the spectrum contains the characteristic peak of the 1H species at ∼975 cm−1, showing the existence of 1H-1,2,3-triazole on the surface.21 Besides, only one peak (1240 cm−1), instead of two peaks, is observed between 1210 and 1260 cm−1 in the 120 E


F

a

889 838 797 698

νrg, δrg, δCC

δrg ωCH ωCH ωCH

953

889 838 786 702 705

806

933

956

977

1141 1095

1224

1387

1417

1446

1539

3126 3010 2868

190 K

1.0 L

975

1168 1107

1442

380 K

802 792

954

975

1164 1110

1245

1421

1442

3155 3022 2896

120 K

975

1164

1442

380 K

0.5 L

800 773

963

1068

1146 1097

1230

1412

1439

1,2,3-triazolec anion (aq)

ω(CH) τ(ring)

ν(CC), δ(CH) ν(NN), δ(ring) ν(NN), δ(CH) δ(ring)

ν(NN), ν(CN)

ν(CN), δ(CH)

ν(CC)

modec

756

912

937

986

1066

1157 1100

1210

1355

1437

1,2,3-triazolated/Cu(100) (calculated)

Reference 21. bThis experimental work. cReference 22. dThis theoretical work. eν: stretching, δ: in-plane bending, ω: out-of-plane bending, rg: ring, and τ: torsion.

δrg ωCH ωCH ωCH 883 819 794 702

956

953

νrg, δrg

976 νrg, δrg

975

νrg, δCH

1079

1078

1223 1132 1093

νrg νrg, δCH νrg, δrg

1114

νrg, δCH νrg, δCH νrg, δCH

1241

1071

1240

νrg, δCH, δNH νrg, δCH

1380

1149 1114

1250

1380

1539

1421

1419

1419

νCH νrg, δNH, δrg

3157 3020 2904

120 K

νrg, δCH

3123 1525

νCH νrg, δCH, δNH

3123 1525

νCH νCH

modea

νrg, δCH, δNH νrg, δCH, δNH νrg

3146 3123

νCH νCH

modea

2H-1,2,3-triazole (liquid)

3146 3123

1H-1,2,3-triazole (liquid)

1H-1,2,3-triazole/Cu(100)b

Table 1. Comparison of the IR Frequencies (cm−1) of 1H-1,2,3-Triazole, 2H-1,2,3-Triazole, and 1,2,3-Triazolatee

ωCH

δ(CH), ν(NN) δ(CH), ν(NN) δ(CH), δ(ring)

ring breathing δ(CH), ν(CC) δ(CH)

ν(CN), δ(CH) ν(NN)

ν(CN), ν(CC)

moded

The Journal of Physical Chemistry C Article


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Figure 6. Temperature-dependent RAIRS spectra of 0.5 L of 1H-1,2,3-triazole on Cu(100). All of the spectra were measured at ∼120 K. The 1H1,2,3-triazole molecules were adsorbed at ∼120 K, followed by progressively heating the surface to the temperatures indicated.

Figure 7. (a,b) NEXAFS of 0.5 L of 1H-1,2,3-triazole on Cu(100) at 120 and 380 K. All of the spectra were measured at ∼120 K. The triazole molecules were adsorbed at 120 K, followed by heating the surface to 380 K. (c,d) show the normalized peak intensities of 400.4 and 400.9 eV as a function of the light incidence angle, respectively, and the fitting curves.

1146 cm−1. Raising the surface temperature to 190 K can also cause changes in the adsorption layer, including H-bonding between the adsorbates and molecular adsorption orientation, resulting in the change of IR absorption behavior of the adsorbed triazole molecules. The observed peak frequencies in the 190 K spectrum are also listed in Table 1. The strong, broad 883 cm−1 peak at 120 K, which is likely due to highly associated 1H-1,2,3-triazole molecules, disappears at 190 K because of the decreased concentration of the triazole molecules from partial desorption and dissociation. There is the strongest, broad 806 cm−1 peak in the 190 K spectrum, which can be assigned to the out-of-plane CH (ω(CH)) bending mode of 1H-1,2,3-triazole. According to the surface dipole selection rule of RAIRS, this ω(CH) would be largely enhanced with the triazole ring parallel to the Cu(100) surface, that is, with the C−H bonds lying fat.34 Therefore the temperature-dependent IR changes from 120 to 190 K suggest

K spectrum, which is consistent with the IR absorption behavior of the 1H species.21,23 As a contrast, 2H-1,2,3-triazole is expected to have two IR peaks in this range. Note that because of the similar structures of 1H- and 2H-1,2,3-triazole, they have common, unresolved peaks or small frequency differences for similar vibrational modes (Table 1). It is suggested that 1H-1,2,3-triazole likely predominantly exists on Cu(100) at 120 K, although the adsorption of its 2H tautomer cannot be completely ruled out. In Figure 5, the IR absorption behavior changes significantly upon heating to 190 K. At 190 K, partial desorption of the triazole from the multilayer and of H2 occurs (Figure 3). As compared to the relatively weak peaks observed at higher temperatures (380−490 K), which are from dissociated 1H1,2,3-triazole, the 190 K spectrum is mainly due to the intact triazole molecules, and dissociated 1H-1,2,3-triazole may contribute in part to the absorptions at ∼977, 1168, and G


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Figure 8. (a,b) NEXAFS of 0.05 L of 1H-1,2,3-triazole on Cu(100) at 120 and 380 K. All of the spectra were measured at ∼120 K. The triazole molecules were adsorbed at 120 K, followed by heating the surface to 380 K. (c,d) show the normalized peak intensities of 400.4 and 400.9 eV as a function of the light incidence angle, respectively, and the fitting curves.

NEXAFS. NEXAFS experiments have been performed to study the changes in the structure and adsorption geometry of 1H-1,2,3-triazole on Cu(100) from 120 to 380 K at two different exposures of 0.5 and 0.05 L. Note that the surface is mainly covered with 1H-1,2,3-triazole molecules at 120 K. Figure 7a shows the near nitrogen K-edge X-ray absorption spectra of 0.5 L of 1H-1,2,3-triazole on Cu(100) (120 K), measured at the indicated light incidence angles (θ) with respect to the surface. Four features appear at 400.4, 402.0, 406.6, and 412.5 eV in these spectra, with the first two assigned to N1s → π* transition and the other two to N1s → σ*.35 In the NEXAFS study of a 1,2,3-triazole ring with the 1N and 4C atoms attaching to alkyl groups, three π* resonance features have been detected at 399.7, 400.3, and 401.6 eV, being assigned to 2N, 3N, and 1N atoms, respectively.13 Therefore, the 402.0 eV peak in Figure 7a is assigned to the 1N of 1H1,2,3-triazole and the 400.4 eV peak, with nearly twice the intensity, to the 2N and 3N atoms. It is also found that the π*feature intensities seem to gradually decrease toward higher incidence angles. As the 1H-1,2,3-triazole-covered surface is heated to 380 K, the π* resonance becomes a predominant broad peak at 400.9 eV, as shown in Figure 7b. Besides, this feature has a trend to grow with increasing incidence angles, which is different from the case before surface heating (120 K, Figure 7a). These changes can be explained by the N1−H bond scission of 1H1,2,3-triazole to generate 1,2,3-triazolate, leading to the variation of the −NH− and −N functionalities and by different adsorption orientations of these two surface species. To more clearly analyze the adsorption geometries, the peak intensity of 400.4 eV in Figure 7a and the peak intensity of 400.9 eV in Figure 7b are normalized and plotted as a function of the incidence angle, as shown in Figure 7c,d, respectively. These data points can be fitted to make an estimation for the adsorption orientations of 1H-1,2,3-triazole and 1,2,3-triazolate, with the equation of I(θ,α) ≈ P(sin2 α sin2 θ + 2 cos2 α cos2 θ) + (1 − P) sin2 α, where I is the normalized intensity, α

that the triazole rings for the adsorbed 1H-1,2,3-triazole at 190 K seem to have a smaller tilting angle with respect to the surface, on average, as compared to that of the 1H-1,2,3triazole at 120 K. In Figure 5, the IR spectra in the temperature range of 380−490 K show peaks at 975, 1107, 1168, and 1142 cm−1, which are attributable to dehydrogenated 1H-1,2,3triazole, from N−H bond scission. It is also found that the dehydrogenated 1H-1,2,3-triazole peaks agree well with those of the 1,2,3-triazole anion (i.e., 1,2,3-triazolate) present in the aqueous solution of pH 12, as shown in Table 1.22 Accordingly, the peaks of the adsorbed 1,2,3-triazolate can be assigned as follows: 975 cm−1 to δ(ring), 1107 cm−1 to ν(NN) and δ(ring), 1168 cm−1 to ν(CC) and δ(CH), and 1442 cm−1 to ν(CC). Only the stretching modes of C−C and N−N and the in-plane bending modes of C−H and ring are detected in this case, with no appearance of the out-of-plane CH bending peak expected to be at ∼800 cm−1 (Table 1). This result excludes the possibility for the adsorbed 1,2,3triazolate with its ring parallel to the surface in terms of the dipole selection rule.34 The triazolate peaks can also been seen in the 230 K spectrum (Figure 5), with other small absorptions possibly from residual 1H-1,2,3-triazole, but they completely vanish at 610 K. Figure 6 shows the temperature-dependent RAIRS spectra of 0.5 L of 1H-1,2,3-triazole on Cu(100). No multilayers are formed at this exposure (Figure 1). The IR peaks belonging to 1H-1,2,3-triazole appear at 792, 802, 954, 975, 1110, 1245, 1421, 1442, 2896, 3022, and 3155 cm−1 in the 120 K spectrum. Similarly, the N−H stretching mode is not observed either. At 120 K and a lower coverage of 0.5 L, formation of 1,2,3triazolate is evidenced by the peaks of 1164 and 1442 cm−1. Upon heating the surface to 200 K, these two peaks grow because of the increase of 1,2,3-triazolate. Besides, a tiny amount of 1H-1,2,3-triazole is left at 200 K, with a weak band at 954 cm−1. From 240 to 470 K, the surface is only covered with 1,2,3-triazolate. H


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The Journal of Physical Chemistry C is the angle of the triazole rings relative to the surface, and P is the degree of linear polarization of the synchrotron radiation.35,36 On the basis of the fitting results, the 1H1,2,3-triazole molecules in the 120 K adsorption layer from 0.5 L exposure have an average tilting angle between ∼45° and 55o, and 1,2,3-triazolate (380 K) has a larger angle in the range of 70°−90°, near an upright adsorption geometry. Figure 8 shows the NEXAFS spectra and fitting results at 0.05 L of 1H-1,2,3-triazole, with similar experimental conditions and fitting procedure as those for Figure 7. At this low coverage, the π* features of 400.4 and 402.0 eV signify the presence of 1H-1,2,3-triazole on Cu(100) at 120 K, which becomes 1,2,3-triazolate (400.9 eV) at 380 K. This chemical change is also observed at 0.5 L, however, the average ring tilting angle of the adsorbed 1H-1,2,3-triazole at 120 K increases to be in the range of ∼60°−70°. The surface 1H1,2,3-triazole molecules in the adsorption layer at higher coverages can develop a strong hydrogen-bonding network to minimize the energy, therefore resulting in a more parallel adsorption orientation. The adsorbed 1,2,3-triazolate at 0.05 L (380 K) also has a nearly upright orientation. Theoretical Calculations for the Adsorption Structures of 1H-1,2,3-Triazole and 1,2,3-Triazolate on Cu(100). Shown in Figure 9 is the calculated adsorption

the triazole, the bonding mainly results from the electrostatic dipole interaction. At the physisorption state, the molecule tends to be adsorbed in parallel, possibly due to the πinteraction, with a much lower adsorption energy.37,38 Upon dehydrogenation of 1H-1,2,3-triazole on Cu(100) and formation of 1,2,3-triazolate, this intermediate is also theoretically predicted to be perpendicularly adsorbed (Figure 10) via two nitrogen atoms (2N and 3N in this case). d(2N−

Figure 10. Calculated adsorption structure of 1,2,3-triazolate on Cu(100), with two viewing angles and tabulated structural parameters.

Cu(s)) is reduced to 1.895 Å, indicating stronger bonding to the surface with respect to 1H-1,2,3-triazole. Because of this enhanced surface interaction, d(2N−3N) of 1,2,3-triazolate is increased by 0.022 Å, as compared to that of 1H-1,2,3-triazole. The other four bonds are subjected to changes in the length because of N−H bond scission, including the largely reduced d(1N−2N) at 1.318 Å. The theoretically predicted, upright 1,2,3-triazolate orientation is consistent with the NEXAFS result (Figures 7 and 8). Moreover, the IR peaks and the corresponding modes for the upright 1,2,3-triazolate have been calculated and included in Table 1 for comparison, which agree with the IR absorptions observed in Figures 4 and 5. Because of the symmetric structure of 1,2,3-triazolate itself, there are two identical adsorbed triazolates, with the 1N and 2 N atoms or 2N and 3N atoms bonding to the surface (Figure 11). Coexistence or interchange of these two surface 1,2,3triazolate isomers, with the 1N, 2N, and 3N as the bonding sites, can explain why only one N1s emission peak at 400.2 eV (Figure 4) and one π* feature at 400.9 eV (Figure 7) are detected. Theoretically, the transformation between the 1,2,3triazolate twins has been calculated, with the reaction path and structure of the TS shown in Figure 11. The activation of this process is calculated to be 8.7 kcal mol−1, which is not large, suggesting that the interchange is feasible. There are other possible origins leading to one N1s emission peak and one π* feature that cannot be ruled out for the 1,2,3-triazolate. This intermediate is bonded to the surface by two nitrogen atoms, however, with a similar electronic structure for all three nitrogen atoms, or the adsorption of this intermediate induces a local structure change near the bonding site, resulting in that the three nitrogen atoms become differentiable by XPS and NEXAFS.

Figure 9. Calculated adsorption structure of 1H-1,2,3-triazole on Cu(100), with two viewing angles and tabulated structural parameters.

structure of 1H-1,2,3-triazole on Cu(100), without considering the interaction between the adsorbates. The optimized structure has a perpendicular orientation, attaching to the surface via the 2N and 3N atoms close to two atop sites. The 2 N−3N has a shortest length (1.330 Å) in the ring, as compared to the longest 4C−5C at 1.380 Å. The distance between 2N and the copper surface (d(2N−Cu(s))) is 1.985 Å. This theoretical result can explain the observed larger ring tilting angle for the adsorbed 1H-1,2,3-triazole at the low coverage of 0.05 L (Figure 8), as compared to the higher exposure case of 0.5 L (Figure 7), preventing significant intermolecular H-bonding interaction. The adsorption geometry and energy of 1H-1,2,3-triazole on Cu(111) have been calculated using DFT.37,38 At the chemisorption state, the molecule is predicted to be adsorbed perpendicularly with an adsorption energy of 0.50−0.55 eV, depending on the bonding nitrogens and sites.37,38 Because of the large dipole moment of I


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Scheme 2. Suggested Ring Rupture for the Formation of HCN, N2, and CH3CN from the Decomposition of 1,2,3Triazolate on Cu(100)

Figure 11. Transformation path of the two isomeric 1,2,3-triazolates on Cu(100) and the structure of the TS.

Reaction Pathway of 1H-1,2,3-Triazole on Cu(100). The primary reaction of 1H-1,2,3-triazole proceeds by N−H cleavage, forming 1,2,3-triazolate on the surface. At a low coverage (0.05 L), the generated surface H atoms (H(ad)) recombine to be the H2 product at ∼310 K. However, at higher exposures, H2 formation is shifted to ∼170 K with a different mechanism from the self-coupling of H(ad). Two possible mechanisms for the low-temperature channel occurring at higher coverages are proposed in Scheme 1. Scheme 1. Proposed Mechanisms for the H2 Formation from 1H-1,2,3-Triazole on Cu(100) at ∼170 K

Figure 12. TPR/D spectra of 1.0 L of 1H-1,2,3-triazole on O/ Cu(100).

350 K is no longer observed but with H2O evolution at 207 K. This result is explained by the reaction of O(ad) with the N−H of the triazole molecule, forming OH(ad). Self-coupling of the OH groups on Cu(100) occurs at 207 K to evolve H2O.39 1,2,3-Triazolate is formed on the surface, shown later by RAIRS, after the deprotonation reaction. The evolution of the reaction products from the triazolate on O/Cu(100) is divided into two groups at ∼465 and 540 K. The first group (∼465 K) includes H2 (m/z 2), H2O (m/z 18), N2 (m/z 14, 28), and CO2 (m/z 44). Besides, CO is also formed and contributes to the m/z 28 intensity, according to the known intensity ratio of m/z 44/m/z 28 for CO2 and that of m/z 14/m/z 28 for N2 in our system. The small traces of 40 and 41 amu could be due to a vinylideneamine or 1H-azirine species, with the structures shown in Scheme S2. In the previous studies of flash vacuum pyrolysis for alkyl and/or phenyl-substituted 1H-1,2,3-triazoles, substituted vinylideneamines and cyclic 1H-azirines have been proposed as the reactive intermediates after N2 is extruded from the triazole rings.40 The main products in the second group (∼540 K) include H2, N2, HCN, and CH3CN, which evolve at a similar temperature to the case of the 1,2,3triazolate reaction on a bare Cu(100) surface (∼560 K, Figures 2 and 3). In addition to this similarity in the desorption

The H2 may be from the reaction between two adjacent 1H1,2,3-triazole molecules. The other mechanism is the reaction between the 1H-1,2,3-triazole and the H atom from dehydrogenation of another molecule. The 1,2,3-triazolate on Cu(100) decomposes at ∼550 K to form HCN, N2, and CH3CN. These products are suggested to be originated from preferential bond-breaking steps in the triazole ring, as suggested in Scheme 2. Effect of Preadsorbed Oxygen on the Reaction of 1H1,2,3-Triazole/Cu(100). Figures 12 and 13 show the TPR/D spectra of 1.0 L and 0.1 L of 1H-1,2,3-triazole on oxygen precovered on Cu(100), respectively. In the 1.0 L case, desorption of a part of the triazole molecules at 204 K can be seen in the spectra of m/z 28, 40, and 41. H2 formation below J


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Figure 14. Temperature-dependent RAIRS spectra of 1.0 L of 1H1,2,3-triazole on O/Cu(100).

CN, −N−CN, −NCN−, >CCN−, −CN N, −NNN, >CCO, and so forth, with their stretching frequencies reported roughly in the range of 1900−2300 cm−1.41 Because vinylideneamine or 1H-azirine is likely formed at ∼467 or 530 K (Figures 12 and 13), the peaks of 1986, 2152, and 2173 cm−1 may be related to C CN and C−CN containing surface fragments. On comparison of the RAIR spectra of 1,2,3-triazolate on Cu(100) and O/Cu(100), for example, the 430 K spectrum of Figure 5 and the 420 K one of Figure 14 at 1.0 L, it seems that the latter 1,2,3-triazolate has lower peak intensities, which could be due to the electronic effects of the adsorbed oxygen on the IR absorption coefficients and/or on the adsorption orientation of the 1,2,3-triazolate.

Figure 13. TPR/D spectra of 0.1 L of 1H-1,2,3-triazole on O/ Cu(100).

temperature, the relative peak intensities of HCN, N2, and CH3CN in the second group are also similar to those of 1,2,3triazolate on Cu(100) without oxygen. Therefore, it can be concluded that the residual 1,2,3-triazolate further reacts on the surface at ∼540 K, once the preadsorbed oxygen atoms are almost consumed in the reaction with the surface 1,2,3triazolate at ∼465 K. In the reaction of 0.1 L of 1H-1,2,3-triazole on O/Cu(100) (Figure 13), no triazole desorption is observed at this low exposure. The O(ad) abstracts the H from the NH group of 1H1,2,3-triazole and results in the H2O evolution at 218 K, without H2 below 350 K. The reaction of O(ad) and 1,2,3triazolate also occurs at ∼465 K and produces H2, H2O, N2, CO, and CO2. The relatively small peak at 527 K in the m/z 40 trace is attributable to 1H-azirine or vinylideneamine. Moreover, H2, HCN, and N2 are found at ∼560 K. Interestingly, CH3CN formation is terminated, suggesting that the products at ∼560 K may not be directly from 1,2,3-triazolate but due to reaction fragments from the 1,2,3-triazolate ring rupture. This pathway may also occur in the 1.0 L case (Figure 12). The possible surface intermediates generated from the triazolate ring dissociation, with RAIRS evidence, are shown later. IR Study of 1H-1,2,3-Triazole on O/Cu(100). Shown in Figure 14 are the temperature-dependent RAIRS spectra of 1.0 L of 1H-1,2,3-triazole on O/Cu(100). The absorptions in the 120 and 190 K spectra are mainly because of the adsorbed triazole molecules. Upon heating to 240 K, desorption and deprotonation of 1H-1,2,3-triazole leads to appearance of the absorption features of 975, 1170, and 1446 cm−1 belonging to 1,2,3-triazolate, which still exists on the surface at 420 K. In the 490 K spectrum, the three triazolate peaks are present, with three other absorptions at 1986, 2152, and 2173 cm−1. As shown in Figure 12, the reaction between the adsorbed oxygen and 1,2,3-triazolate proceeds at ∼460 K; therefore, the three peaks above 1900 cm−1 must be from the opening of the triazole ring and are assignable to triple bonds (XY−Z) or cumulated double bonds (XYZ), such as −CC−, −C−

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SUMMARY As shown in Scheme 3, the reaction of 1H-1,2,3-triazole on Cu(100) starts with N−H bond dissociation, producing H2 at Scheme 3. Proposed Reaction Pathways of 1H-1,2,3Triazole

∼300 or ∼170 K, which depends on the coverage and results from different mechanisms. The 1,2,3-triazolate is proposed to be adsorbed perpendicularly (or nearly perpendicularly) on Cu(100). The triazolate further reacts on the surface to generate H2, HCN, N2, and CH3CN at ∼550 K. With preadsorbed oxygen atoms on Cu(100), 1H-1,2,3-triazole deprotonates first and also produces 1,2,3-triazolate on the surface. On O/Cu(100), no H2 evolves below 350 K, whereas H2O is formed at ∼210 K. The triazolate decomposes at a K


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The Journal of Physical Chemistry C lower temperature of ∼460 K to form gaseous products of H2, N2, HCN, H2O, CO, and CO2, possibly with C−CN and/or CCN containing intermediates on the surface, which further react to generate H2, HCN, and 1H-azirine (or vinylideneamine). On the basis of our results of 1H-1,2,3triazole on Cu(100) and O/Cu(100), chemisorbed triazole and triazolate can be the active surface species in copper corrosion inhabitation. The triazolate can be stable up to ∼500 K on copper but possibly be lowered by ∼50 K on the oxidized surfaces. Triazolate species are potential candidates to form SAMs, with C4−X and C5−Y as the terminal functional groups for surface property tailoring.

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pyridyl-1,2,3-triazole ligands: Synthesis, X-ray structures and copper(II) and silver(I) complexes. Polyhedron 2010, 29, 70−83. (8) Guha, P. M.; Phan, H.; Kinyon, J. S.; Brotherton, W. S.; Sreenath, K.; Simmons, J. T.; Wang, Z.; Clark, R. J.; Dalal, N. S.; Shatruk, M.; et al. Structurally Diverse Copper(II) Complexes of Polyaza Ligands Containing 1,2,3-Triazoles: Site Selectivity and Magnetic Properties. Inorg. Chem. 2012, 51, 3465−3477. (9) Uddin, M. N.; Siddiquey, I. A.; Islam, M. J.; Fouad, O. A.; Nagano, M. 1H-1,2,3-Triazole, a Promising Precursor for Chemical Vapor Deposition of Hydrogenated Carbon Nitride. J. Cryst. Growth 2009, 311, 3528−3532. (10) Ofoegbu, S. U.; Galvão, T. L. P.; Gomes, J. R. B.; Tedim, J.; Nogueira, H. I. S.; Ferreira, M. G. S.; Zheludkevich, M. L. Corrosion Inhibition of Copper in Aqueous Chloride Solution by 1H-1,2,3Triazole and 1,2,4-Triazole and Their Combinations: Electrochemical, Raman and Theoretical Studies. Phys. Chem. Chem. Phys. 2017, 19, 6113−6129. (11) Díaz, D. D.; Punna, S.; Holzer, P.; McPherson, A. K.; Sharpless, K. B.; Fokin, V. V.; Finn, M. G. Click Chemistry in Materials Synthesis. 1. Adhesive Polymers from Copper-Catalyzed Azide-Alkyne Cycloaddition. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 4392− 4403. (12) Collman, J. P.; Devaraj, N. K.; Eberspacher, T. P. A.; Chidsey, C. E. D. Mixed Azide-Terminated Monolayers: A Platform for Modifying Electrode Surfaces. Langmuir 2006, 22, 2457−2464. (13) Darlatt, E.; Nefedov, A.; Traulsen, C. H.-H.; Poppenberg, J.; Richter, S.; Dietrich, P. M.; Lippitz, A.; Illgen, R.; Kühn, J.; Schalley, C. A.; et al. Interpretation of Experimental N K NEXAFS of Azide, 1,2,3-Triazole and Terpyridyl Groups by DFT Spectrum Simulations. J. Electron Spectrosc. Relat. Phenom. 2012, 185, 621−624. (14) Ciampi, S.; Böcking, T.; Kilian, K. A.; James, M.; Harper, J. B.; Gooding, J. J. Functionalization of Acetylene-Terminated Monolayers on Si(100) Surfaces: A Click Chemistry Approach. Langmuir 2007, 23, 9320−9329. (15) Guan, B.; Ciampi, S.; Le Saux, G.; Gaus, K.; Reece, P. J.; Gooding, J. J. Different Functionalization of the Internal and External Surfaces in Mesoporous Materials for Biosensing Applications Using ″Click″ Chemistry. Langmuir 2011, 27, 328−334. (16) Stenehjem, E. D.; Ziatdinov, V. R.; Stack, T. D. P.; Chidsey, C. E. D. Gas-Phase Azide Functionalization of Carbon. J. Am. Chem. Soc. 2013, 135, 1110−1116. (17) Bebensee, F.; Bombis, C.; Vadapoo, S.-R.; Cramer, J. R.; Besenbacher, F.; Gothelf, K. V.; Linderoth, T. R. On-Surface AzideAlkyne Cycloaddition on Cu(111): Does It ″Click″ in Ultrahigh Vacuum? J. Am. Chem. Soc. 2013, 135, 2136−2139. (18) Winnewisser, M.; Vogt, J.; Ahlbrecht, H. Gas Phase Pyrolysis of 1,2,3-Triazole. J. Chem. Res., Synop. 1978, 298−299. (19) Bock, H.; Dammel, R.; Aygen, S. Gas-Phase Reactions. 36. Pyrolysis of Vinyl Azide. J. Am. Chem. Soc. 1983, 105, 7681−7685. (20) da Silva, G.; Bozzelli, J. W. Retro-[3 + 2]-Cycloaddition Reactions in The Decomposition of Five-Membered NitrogenContaining Heterocycles. J. Org. Chem. 2008, 73, 1343−1353. (21) Billes, F.; Endrédi, H.; Keresztury, G. Vibrational Spectroscopy of Triazoles and Tetrazole. J. Mol. Struct.: THEOCHEM 2000, 530, 183−200. (22) Toernkvist, C.; Bergman, J.; Liedberg, B. Correlated ab Initio Geometries and Vibrations of 1H- and 2H-1,2,3-Triazole. J. Phys. Chem. 1991, 95, 3123−3128. (23) Borello, E.; Zecchina, A.; Guglielminotti, E. A Vibrational Assignment for 1,2,3-Triazole. J. Chem. Soc. B 1969, 307−311. (24) Stiefvater, O. L.; Jones, H.; Sheridan, J. Double-ResonanceDouble-Search Assignment of The Microwave Spectrum of 1,2,3Triazole. Spectrochim. Acta, Part A 1970, 26, 825. (25) Sørensen, G. O.; Nygaard, L.; Begtrup, M. Microwave Spectrum of 1-Deuterio-1,2,3-Triazole. J. Chem. Soc., Chem. Commun. 1974, 605−606. (26) Begtrup, M.; Nielsen, C. J.; Nygaard, L.; Samdal, S.; Sjøgren, C. E.; Sørensen, G. O.; Khan, S. I.; Vilkov, L. V.; Rypdal, K. The Molecular Structure and Tautomer Equilibrium of Gaseous 1,2,3-

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.8b08007. Multilayer desorption of 1H-1,2,3-triazole from Cu(100), showing zero-order kinetics; identification of the reaction products from 1H-1,2,3-triazole/Cu(100) by mass-cracking patterns; coordinations of 1,2,3triazolate to metal ions; and structures of vinylideneamine and 1H-azirine (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: 886 6 2757575 ext. 65326. ORCID

Jong-Liang Lin: 0000-0002-1276-5479 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was financially supported by the Ministry of Science and Technology of the Republic of China (MOST 106-2113-M-006-001). We thank Dr. Y.-W. Yang and Dr. C.-H Wang (National Synchrotron Radiation Research Center, Taiwan) for their assistance in obtaining the XPS and NEXAFS data.

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REFERENCES

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