Photoelectron Spectroscopic and Theoretical Study of AromaticâBim

Article pubs.acs.org/JPCA

Photoelectron Spectroscopic and Theoretical Study of Aromatic−Bim Anionic Complexes (Aromatic = C6H5, C5H4N, C4H3O, and C4H4N; m = 1−3): A Comparative Study Zhang Sun,†,§ Shutao Sun,† Hongtao Liu,† Zichao Tang,†,‡ and Zhen Gao*,† †

Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China ‡ State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P. R. China § College of Chemical Engineering, Hebei United University, Tangshan 063009, P. R. China ABSTRACT: The reactions between Bi clusters generated by laser ablation and different aromatic molecules (C6H6, C5H5N, C4H4O, or C4H5N) seeded in argon carrier gas were studied by a reflectron time-of-flight mass spectrometer (RTOF-MS) with a photoelectron spectrometer. The photoelectron (PE) spectra of the dominant anionic products Bim C 6H 5 −, BimC5H4N− (m = 1−4) and BimC4H3O−, BimC4H4N− (m = 1−3) dehydrogenated complexes were obtained by 308 and 193 nm laser, respectively. It was found that the adiabatic electron affinities (EAs) of BimC4H4N are higher than those of BimC6H5, BimC5H4N, and BimC4H3O with the same metal number m. Theoretical calculations with density functional theory (DFT) were carried out to elucidate the possible structures for BimC4H4N− and BimC4H4N complexes. By comparison of the theoretical and experimental EAs, the most possible structures were the isomers in which the C4H4N group binds to metal clusters with the N−Bi bond, and their simulated spectra based on Koopmans’ theorem were in correct agreement with the PES results. Furthermore, the analysis of the molecular orbital composition provided evidence that the C4H4N group contributes a single electron to bind to Bim clusters with the Bi−N σ bond.

1. INTRODUCTION The study of the adsorption of a molecule or fragment on a metal surface is an important subject in surface science. The understanding of the structure and properties of adsorbates on metals can help to develop a microscopic level description of heterogeneous catalysis, organometallic reactions in the condensed phase and electron transfer in biological systems.1,2 In recent years, many experimental3−10 and theoretical11−19 investigations on the interaction of metal clusters with benzene in gas phase have been extensively reported. Furthermore, some studies of [Mmphenyl]− complexes were also reported. Xing et al.20 reported the generation of [Mmphenyl]− (M = Mn−Cu) complexes. The phenyl-coinage metal complexes (AgmC6H5−, AumC6H5−, m = 1−3)21 and phenyl−lead metal complexes (PbmC6H5−, m = 1−5)22 were studied by photoelectron spectroscopy (PES) and density functional theory (DFT). While these studies focused mainly on the reactions of metal species with benzene molecule, the researches are still required on the reactions of main group metal clusters with heterocyclic aromatic molecules. Heterocyclic aromatic molecules are one part of the most important organic molecules in chemistry and biology. The study on heterocyclic aromatic molecules is of great significance in biochemistry and pharmacy.23,24 Furan and pyrrole are fivemembered heterocycles and are prone to electrophilic © XXXX American Chemical Society

substitution. The C−H and N−H activations of aromatic compounds were studied experimentally25 and theoretically.26,27 It has been shown that the N−H bond activation is both kinetically and thermodynamically preferred to C−H activation. However, the interactions of metal clusters with the heterocyclic aromatic molecules have been less reported. Our group reported a spectroscopic and theoretical study of aromatic−Pbm anionic complexes (aromatic = C6H5, C5H4N, C4H3O, and C4H4N) and showed that C4H4N group binds to lead clusters with Pb−N σ bond in PbmC4H4N−(m = 1−3) dehydrogenated complexes.28 Bismuth, the heaviest group-V element, has one more electron than lead atom. Our group reported BimC6F5 (m = 1−4) anionic complexes by PES and DFT,29 and there are few reports about the interactions between bismuth anionic clusters and aromatic molecules. We need more information about the interactions of heavy metal clusters with heterocyclic aromatic molecules. In the article, we reported an anion photoelectron spectroscopic and density functional theoretical study on Bi m C 6 H 5 − , Bi m C 5 H 4 N − (m = 1−4) and Bi m C 4 H 3 O − , BimC4H4N− (m = 1−3) dehydrogenated complexes, which Received: February 2, 2013 Revised: April 29, 2013

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dx.doi.org/10.1021/jp401222k | J. Phys. Chem. A XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry A

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were produced from reactions between aromatic molecules (C6H6, C5H5N, C4H4O, or C4H5N) and Bi clusters generated by laser ablation on Bi solid sample. By combination of experimental and theoretical studies, we have obtained some important information about the bonding and geometric and electronic structures of the BimC4H4N− complexes.

2. EXPERIMENTAL METHODS The apparatus used in the experiments mainly consists of a homemade reflectron time-of-flight mass spectrometer (RTOFMS) and a photoelectron spectrometer with magnetic-bottle type analyzer. The detail of the apparatus has been described elsewhere,30,31 and only an outline is given below. A rotating Bi metal disk target (purity > 99.99%) in the source chamber of RTOF-MS was ablated by a pulsed laser beam (1064 or 532 nm Nd:YAG laser, 5 Hz, ∼10 mJ/pulse). The laser-induced plasma was carried by molecular beam generated with a pulsed valve at a backing pressure of about 400 kPa of argon (purity 99.99%), seeded with C6H6, C5H5N, C4H4O, or C4H5N, respectively. The ratio of aromatic molecules in the mixed gas was about 0.1% by volume. The aromatic−Bim anionic products from the reactions of Bi plasma and aromatic molecules were entrained by the carrier gas and underwent low pressure (10−2 Pa) expansion in the source chamber. After passing a skimmer, all products entered into the acceleration area in the spectroscopic chamber of RTOF-MS (10−4 Pa). The anionic clusters were accelerated in the direction perpendicular to the molecular beam and then were reflected toward the detector, double microchannel plates (MCP). The resolution (M/ΔM) of RTOF-MS is better than 2000, so it is easy to resolve the number of hydrogen atoms in the products. The anionic products were mass selected by the timing probe and were photodetached by an excimer laser (XeCl 308 nm or ArF 193 nm). The photoelectrons detached were measured by the photoelectron (PE) spectrometer, a magnetic-bottle timeof-flight analyzer. The PE spectrum was calibrated by the known spectra of Cu−, Ag−, and Au−. The energy resolution of the photoelectrons is about 70 meV for electrons with 1 eV kinetic energy. However, the resolution is getting worse as the kinetic energy of the photoelectrons increases.

Figure 1. Measured mass spectra of the anionic products from the reactions between Bi clusters generated by laser ablation and aromatic molecules (a, C6H6; b, C5H5N; c, C4H4O; d, C4H5N) seeded in argon carrier gas (0.1% aromatic molecules in 400 kPa mixed gas).

aromatic molecules (a, C6H6; b, C5H5N; c, C4H4O; d, C4H5N) seeded in argon carrier gas, respectively. All the mass spectra were calibrated carefully according to the mass numbers of pure metal clusters. The resolution of the mass spectrometer is enough to assign the products correctly and to resolve the hydrogen distribution. As shown in Figure 1, the dominant anionic products of the reactions between Bi clusters with C6H6, C5H5N, C4H4O, and C4H5N, respectively, are BimC6H5− (m = 1−6), BimC5H4N− (m = 1−5), BimC4H3O− (m = 1−5), and BimC4H4N− (m = 1−4) dehydrogenated complexes. The formation mechanism of the above species probably involves the selective cleavage of C−H or N−H bond in aromatic ring, similar to the formation of the Pbm−phenyl complexes, discussed in our former publication.6 4.2. Photoelectron Spectra with 308 and 193 nm Photons. The photoelectron spectra of BimC6H5− (m = 2−4), BimC5H4N− (m = 1−4), and BimC4H3O− and BimC4H4N− (m = 1−3) at 308 nm (4.03 eV) photon are shown in Figure 2. As shown in Figure 2, the evaluated EA of the corresponding complexes is indicated with the arrow. The evaluation has considered the instrumental resolution (70 meV/1 eV). From

3. COMPUTATIONAL METHODS The geometric optimization for all possible structures of the products was performed with relativistic density functional calculations at the level of generalized gradient approach, using a Perdew−Wang exchange-correlation functional.32 The zeroorder regular approximation Hamiltonian was used to account for the scalar (mass velocity, Darwin, and spin−orbit) relativistic effects.33 The standard Slater-type orbital basis sets of the triple-ζ plus two polarization functions (TZ2P) were used for the orbitals of Bi, C, N, O, and H atoms, and the frozen core (1s2−4f14) approximation was used for Bi. All the calculations were accomplished with the Amsterdam Density Functional (ADF 2005) programs.34 It has been indicated that these theoretical methods are suitable for the study on the metal clusters.35−37 4. RESULTS AND DISCUSSION 4.1. Mass Spectrum. Figure 1 shows the typical mass spectra of the anionic products generated from the reactions between Bi clusters generated by laser ablation and different B



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Figure 2. Photoelectron spectra of BimC6H5− (m = 2−4), BimC5H4N− (m = 1−4), and BimC4H3O− and BimC4H4N− (m = 1−3) at 308 nm (4.03 eV) photon.

close with each other, and the difference is about 0.05 eV. However, the EAs of BimC4H4N are higher than the others, and the difference is over 0.2 eV, especially 0.6 eV for Bi2C4H4N. It has been reported that the C6F5 group binds to Bi clusters through Bi−C σ bond for BimC6F5− complexes.29 For BimC6H5−, BimC5H4N−, and BimC4H3O− complexes, Bi clusters might replace H atom of C6H6, C5H5N, and C4H4O to form dehydrogenated complexes with Bi−C bond. However, C4H5N has three kinds of H atoms, and one binds to N with an N−H bond. The higher EAs of BimC4H4N might indicate that the Bi clusters bind to C4H4N group with Bi−N bond since the electronegativity of the N atom (3.04) is larger than that of C atom (2.55).39 In order to confirm the point, we studied the geometric and electronic structures of BimC4H4N− complexes by DFT calculations. 4.3. Low Energy Structures. We considered a variety of structures for both the neutrals BimC4H4N and anions BimC4H4N− (m = 1−3). The optimized possible structures are shown in Figure 4, and their structural energetic characteristics are summarized in Table 2. For BiC4H4N− anion, the lowest-energy structure is C2v symmetry with 2B2 state (I), in which the C4H4N group binds to a metal atom with an N−Bi bond. The o-isomer (II) and m-isomer (III) of anion BiC4H4N−, in which the C4H4N group binds to a metal atom with a C−Bi bond, are 0.32 and 0.68 eV higher in energy than Isomer I, respectively. For isomers of neutral BiC4H4N, their energies are very close, and the difference is about 0.01 eV.

Figure 2, we can see that the EAs of BimC6H5 (m = 2−4), BimC5H4N (m = 1−4), and BimC4H3O and BimC4H4N (m = 1− 3) show the odd−even alternation, in which the species containing even numbers of metal atoms exhibit higher electron binding energies than the ones containing odd numbers of metal atoms. This result can be explained by the electron pairing effect, just like the pure Bi clusters, in which the EA of the odd numbered pure metal cluster is larger than that of the even one.38 The photoelectron (PE) spectra of BimC6H5−, BimC5H4N− (m = 1−4) and BimC4H3O−, BimC4H4N− (m = 1−3) at 193 nm (6.42 eV) photon are shown in Figure 3. The PE spectra at 193 nm photon show more electronic information because the 193 nm photon (6.42 eV) has higher energy than 308 nm photon (4.03 eV). However, the resolution of the spectra obtained with 193 nm photon is worse than that of the spectra at 308 nm photon, especially for the low binding energy sides of the spectra. It can be seen that the PE spectra of aromatic−Bim have a similar character for different aromatic groups, as shown in Figures 2 and 3. The distributions of the PE spectra for one Bi atom binding to different aromatic groups are very similar, and their PE spectra all present three peaks in the low binding energy side. The fact indicates that the PE spectra show the electron structures of Bi clusters. The affirmed electron affinities of aromatic−Bim (aromatic = C6H5, C5H4N, C4H3O, C4H4N, m = 1−3) at 308 and 193 nm photons are shown in Table 1. As shown in Table 1, it is clear that the EAs of BimC6H5, BimC5H4N, and BimC4H3O are very C



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Figure 3. Photoelectron spectra of BimC6H5−, BimC5H4N− (m = 1−4) and BimC4H3O−, BimC4H4N− (m = 1−3) at 193 nm (6.42 eV) photon.

Table 1. Measured Electron Affinities (EA, eV) for Aromatic−Bim (aromatic = C6H5, C5H4N, C4H3O, C4H4N, m = 1−3) at 308 and 193 nm Photons BimC6H5

BimC5H4N

BimC4H3O

BimC4H4N

m

308 nm

193 nm

308 nm

193 nm

308 nm

193 nm

308 nm

193 nm

1 2 3

1.20 1.62 1.50

1.20 1.62 1.50

1.21 1.68 1.54

1.19 1.67 1.54

1.25 1.68 1.50

1.22 1.65 1.54

1.45 2.25 1.90

1.43 2.23 1.92

Figure 4. Optimized structures for neutrals BimC4H4N (m = 1−3) and anions BimC4H4N− (m = 1−3). See Table 2 for structure parameters. D



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Table 2. Various Structural and Energetic Characteristics of Neutrals BimC4H4N (m = 1−3) and Anions BimC4H4N− (m = 1−3) EA(eV) isomer BiC4H4N

BiC4H4N−

Bi2C4H4N

Bi2C4H4N−

Bi3C4H4N

Bi3C4H4N−

I II III I II III I II III IV I II III IV I II III IV V VI I II III IV V VI

state 3

A2 A″ 3 A″ 2 B2 2 A′ 2 A′ 2 A″ 2 A2 2 A″ 2 A″ 1 A′ 1 A1 1 A′ 1 A′ 1 A′ 1 A1 1 A1 1 A1 1 A′ 1 A′ 2 A″ 2 A2 2 A2 2 B2 2 A″ 2 A′ 3

point group

RN(C)−M1 (Å)

C2v Cs Cs C2v Cs Cs Cs C2v Cs Cs Cs C2v Cs Cs Cs C2v C2v C2v Cs Cs Cs C2v C2v C2v Cs Cs

2.24 2.27 2.27 2.33 2.32 2.32 2.25 2.37 2.27 2.27 2.39 2.84 2.33 2.34 2.28 2.63 2.42 2.29 2.30 2.28 2.34 2.66 2.62 2.41 2.32 2.31

θN(C)−M1−M2 (deg)

ΔE (eV)a

Eb (eV)b

calcd

exptlc

2.37 2.94 2.88 3.10 3.43 3.03 3.00 1.74 3.51 3.51 2.80 1.95 2.83 2.73 2.69 2.64 3.20 2.16 2.95 3.08 2.76 1.77 1.86 2.72 2.83 2.75

1.61 1.22 1.00

1.45

99.1 180 99.5 103.3 105.4 180 97.7 103.4 92 152.7 153.2 180 92.3 95 100.6 150.2 150.5 180 98.5 98.6

0.02 0.00 0.01 0.00 0.32 0.68 0.07 1.27 0.00 0.07 0.00 0.86 0.28 0.52 0.00 1.87 1.38 3.08 0.12 0.08 0.00 1.01 0.92 1.43 0.39 0.49

2.35 2.72 2.00 1.63

2.25

2.02 2.88 2.48 2.63 1.75 1.61

1.92

ΔE is the difference of energy relative to the corresponding lowest lying structure. bEb = E(BimC4H4N(−)) − E(Bim(−)) − E(C4H4N). cThe uncertainty for the experimental EA is ±0.05 eV. a

For anion Bi2C4H4N−, the lowest-energy structure is Cs symmetry with 1A′ state (I), in which the C4H4N group binds to a metal atom with an N−Bi bond, and the angle of N− Bi−Bi is 105.4°. Isomer II of anion Bi2C4H4N−, whose structure is similar to the most possible structure of Pb2C4H4N−,28 is 0.86 eV higher in energy than Isomer I. The o-isomer (III) and m-isomer (IV) of anion Bi2C4H4N−, in which the C4H4N group binds to a metal atom with a C−Bi bond, are much higher in energy than Isomer I. For isomers of neutral Bi2C4H4N, the energies of Isomers I, III, and IV are very close, and the difference is about 0.07 eV. However, Isomer II is higher in energy than them. For anion Bi3C4H4N−, the lowest-energy structure is Cs symmetry with 2A″ state (I), in which the C4H4N group couples on a metal atom through an N−Bi bond. The plane of the C4H4N group is perpendicular to the face of the Bi3 group, and the angle of N−Bi−Bi is 100.6°. For Isomer II, the C4H4N plane is perpendicular to the Bi3 plane; for Isomer III, the C4H4N plane is in the same plane with the Bi3 plane; and for Isomer IV, the linear Bi3 cluster couples on the C4H4N group through an N−Bi bond. They all have much higher energy than Isomer I. The o-isomer (V) and m-isomer (VI) of anion Bi3C4H4N−, in which the C4H4N group couples on a metal atom through a C−Bi bond, are also higher in energy than Isomer I. For neutral Bi3C4H4N, the energies of Isomers I, V, and VI are very close, and the difference is about 0.1 eV. However, the other isomers have higher energy than them.

From above, we can see that the lowest-energy structures of BimC4H4N− (m = 1−3) complexes are the isomers in which the C4H4N binds to metal clusters with the N−Bi bond. Blank et al.25 studied the photodissociation of pyrrole and showed that the dissociation energy of N−H (D0 = 88 kcal/mol) is lower than that of C−H (D0 = 112.5 kcal/mol). Theoretical studies also show that N−H bond activation is both kinetically and thermodynamically preferred to C−H activation.26,27 So for the reaction of Bim− anionic cluster with C4H5N, the most possible way is that Bim− clusters replace the H atom of N−H bond and bind to the C4H4N group with an N−Bi bond to form BimC4H4N− complexes. The electronegativity of the N atom (3.04) is larger than that of C atom (2.55),39 and the N atom has stronger attraction for the valence electrons than C atom. For BimC4H4N− complexes, N atom has stronger attraction for the valence electrons of Bim cluster. Therefore, the EAs of BimC4H4N complexes are higher than those of BimC6H5, BimC5H4N, and BimC4H3O complexes. 4.4. Assignments of the Complex Structures. In the following, we will confirm the structures of BimC4H4N− (m = 1−3) presented in the experiments with the help of relativistic DFT. The assignment of the most possible structures of BimC4H4N−, on the basis of relative energies, and comparisons between the theoretically calculated DOS and the experimental PE spectra is given. This method of structural assignment has been widely used on cluster studies.35,40−42 EA is calculated as the difference between the total energies of the neutral and anion at their respective optimized structures. The theoretical E



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Figure 5. Comparison between PE spectra at 308 and 193 nm photons with the simulated spectra based on Koopmans’ theorem for Isomers I and II of BiC4H4N− anion.

Figure 6. Comparison between PE spectra at 308 and 193 nm photons with the simulated spectra based on Koopmans’ theorem for Isomers I and II of Bi2C4H4N− anion.

the position of the electron binding energy corresponding to each spectrum, not the relative intensity of the spectrum.44 The relative intensity also depends on other factors, such as the unknown orbital-dependent photodetachment cross-section. So here the DOS spectrum is plotted as the stick spectrum by

DOS is shifted by setting HOMO level of the spectra to give the negative of DOS value for the complex. This is called theoretically generalized Koopmans’ theorem (GKT)-shifted43 DOS.44 Here, it should be noticed that, in comparison of the DOS spectrum with the PE spectrum, the important feature is F



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Figure 7. Comparison between PE spectra at 308 and 193 nm photons with the simulated spectra based on Koopmans’ theorem for Isomers I and III of Bi3C4H4N− anion.

Figure 8. Molecular orbital pictures for the most possible structures of BimC4H4N− (m = 1−3) complexes.

spectrum. Thus, we suggest that Isomer I, which is the ground state of anion, contributes to the measured PE spectrum. 4.4.2. Bi2C4H4N−. For Bi2C4H4N− anion, the planar structure (I) with Cs symmetry, in which the C4H4N group binds to the Bi2 cluster with the Bi−N bond, is the lowest-energy structure, and also the calculated EA of Bi2C4H4N by the relativistic DFT is 2.35 eV, which is in correct agreement with the experimental result of 2.25 eV. The comparison of the PE spectrum with the theoretically simulated spectrum based on Koopmans’ theorem for Isomers I and II of Bi2C4H4N− is presented in Figure 6. The distribution of the simulated spectrum of Isomer I agrees correctly with that of the experimental PE spectrum, while Isomer II does not match the experimental PE spectrum. It is suggested that only Isomer I contributes to the measured PE spectrum. 4.4.3. Bi3C4H4N−. The calculations indicate that Isomer I is the lowest-energy structure for both neutral and anion of Bi3C4H4N− complex, and the energies of Isomers II−VI are much higher than that of Isomer I for both neutral and anion. The calculated EAs of isomers I−VI are 2.02, 2.88, 2.48, 2.63, 1.75, and 1.61 eV, respectively, and the experimental result is

aligning the HOMO level of anions with the threshold peak, instead of the fitted DOS spectrum.22,28 The stick spectrum is named the simulated spectrum based on Koopmans’ theorem in the section.29 The comparisons of the simulated spectra based on Koopmans’ theorem with experimental PE spectra of BimC4H4N− (m = 1−3) are shown in Figures 5−7. 4.4.1. BiC4H4N−. The energy difference between the neutral and anionic structures corresponding to the calculated EA is listed in Table 2. The calculated EAs of Isomers I and II of BiC4H4N by the relativistic DFT are 1.61 and 1.22 eV. They are in agreement with the experimental results of 1.45 eV. However, Isomer I with C2v symmetry is the lowest-energy structure of anion BiC4H4N−, in which the C4H4N group binds to the Bi atom with the Bi−N bond and is considered as in the ground state. Figure 5 shows the comparison of the PE spectrum of BiC4H4N− with the simulated spectra based on Koopmans’ theorem of Isomers I and II. The distribution of the simulated spectrum of Isomer I agrees correctly with that of the experimental PE spectrum, while the simulated spectrum for Isomer II is not in agreement with the experimental PE G



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BimC4H4N are higher than those of BimC6H5, BimC5H4N, and BimC4H3O (m = 1−3), which shows that the C4H4N group has stronger interaction with Bim clusters to result in the electron detachment threshold of BimC4H4N− complexes being higher than those of the others. By the relativistic DFT calculations, we elucidated the geometric and electronic structures and bonding of BimC4H4N− complexes. By comparison of the experimentally measured PE spectra and the simulated spectrum based on Koopmans’ theorem by the relativistic DFT, we assigned the most possible structures, and the possible structures of BimC4H4N− (m = 1− 3) are the lowest-energy structures in which the C4H4N group binds to Bim clusters with the Bi−N bond. Furthermore, the analysis of the molecular orbital composition showed that the Bi−N bond in the BimC4H4N− complexes is a σ bond.

1.92 eV. Obviously, the EA of Isomer I is in correct agreement with the experimental result, and the EAs of the other isomers are very far from the experimental value. The simulated spectra based on Koopmans’ theorem of Isomers I and III are compared with the experimental PE spectrum as shown in Figure 7. The distribution of the simulated spectrum of Isomer I agrees reasonably well with that of the experimental PE spectrum, while Isomer III does not match the experimental PE spectrum. So it is suggested that Isomer I is presented in the Bi3C4H4N− anion. 4.5. Orbital Composition and Bonding. We have also analyzed the orbital compositions for the most stable anionic complexes. The molecular orbital (MO) pictures from the calculated BimC4H4N− (m = 1−3) are given in Figure 8. For BiC4H4N−, it is an open-shell structure and has one unpaired electron. The HOMO and HOMO−1 are mostly from the 6px and 6py of Bi atoms, and the energy gap is very small, corresponding to the first peak of PE spectrum (shown in Figure 5). The HOMO−2 and HOMO−3 are from the C4H4N part, and the HOMO−2 and HOMO−3 are corresponding to the second and third peaks of PE spectrum (shown in Figure 5). They are nonbonding MOs for the Bi−N part. The HOMO−4 is formed by interaction from 6s and 6pz of the Bi atom with 9a1 of C4H4N (mainly formed with N, 2pz), and it is a σ MO for the Bi−N part. Therefore, the Bi atom and the C4H4N group bind together with the σ bond in which 6s and 6pz orbits of the Bi atom hybridize and then bind to the 2pz orbit of the N atom. As for Bi2C4H4N−, the HOMO, HOMO−1, and HOMO−3 are mostly from the 6p interaction of the two Bi atoms. The HOMO−2 and HOMO−4 are from the C4H4N part. They are nonbonding MOs for the Bi−N part. The HOMO−5 is formed by interaction from 6s and 6pz of the Bi atom with 9a1 of C4H4N (mainly formed with N, 2pz), and it is a σ MO for the Bi−N part. Therefore, the Bi2 cluster and the C4H4N group bind together with the σ bond in which 6s and 6pz orbits of the Bi atom hybridize and then bind to the 2pz orbit of the N atom. For Bi3C4H4N− anion, the HOMO, HOMO−1, HOMO−2, HOMO−4, and HOMO−5 are mostly the local MOs between Bi atoms (shown in Figure 8). The HOMO−3 and HOMO−6 are from the C4H4N part. Only the HOMO−7 is a σ MO for the Bi−N part, and the inner MOs are nonbonding MOs for the Bi−N part. So we can confirm that the Bi3 cluster connects with the C4H4N group by the Bi−N σ bond in Bi3C4H4N−. The theoretical calculations confirm that an excess electron on the anions binds to the Bim clusters. For each of the BimC4H4N− complexes, there exists only one σ MO for the Bi− N part, which can prove that the C4H4N group binds to the Bi clusters with the Bi−N σ bond. This interaction can also influence the energy level of the outer MOs. Thus, the threshold electron energy of BimC4H4N− complexes is higher than those of Bi m C 6 H 5 − , Bi m C 5 H 4 N − , and Bi m C 4 H 3 O − complexes.

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AUTHOR INFORMATION

Corresponding Author

*(Z.G.) Tel: +86-10-62635054. Fax: +86-10-62563167. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the support of the National Natural Science Foundation of China (Nos. 20203020 and 20433080) and the Scientific Research Foundation for Ph.D. of Hebei United University. We are grateful to Dr. Weijun Zheng and Dr. Jing Wu for their advice on this article.

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REFERENCES

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5. CONCLUSIONS The reactions between Bim clusters generated by laser ablation and different aromatic molecules (C6H6, C5H5N, C4H4O, or C4H5N) seeded in argon carrier gas were studied by a reflectron time-of-flight mass spectrometer with a photoelectron spectrometer. The EAs of the dominant products BimC6H5, BimC5H4N (m = 1−4) and BimC4H3O, BimC4H4N (m = 1−3) were obtained from the photoelectron spectra with 308 and 193 nm photons, respectively. It is found that the EAs of H



Article

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