Single-Molecule Dynamics in the Presence of Strong Intermolecular

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Letter

Single-Molecule Dynamics in the Presence of Strong Intermolecular Interaction Hyun Jin Yang, Michael Trenary, Maki Kawai, and Yousoo Kim J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.6b02053 • Publication Date (Web): 19 Oct 2016 Downloaded from http://pubs.acs.org on October 21, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

Single-Molecule Dynamics in the Presence of Strong Intermolecular Interactions Hyun Jin Yang1,2†, Michael Trenary3, Maki Kawai1 and Yousoo Kim2* 1

Department of Advanced Materials Science, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8561 Japan 2

3

Surface and Interface Science Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

Department of Chemistry, University of Illinois at Chicago, 845 W Taylor Street, Chicago, IL, 60607, USA email: [email protected]

1

Current affiliation: Department of Chemistry and London Centre for Nanotechnology,

University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 17

In contrast to conventional spectroscopic studies of adsorbates at high coverage that provide only spatially-averaged information, we have characterized the laterally-confined shuttling dynamics of a single molecule under the influence of intermolecular interactions by vibrational spectroscopy using a scanning tunneling microscope. The bridge sites on Pt(111) are only occupied by a CO molecule that is surrounded by four other CO molecules at on-top sites. The bridge-site CO undergoes laterally-confined shuttling towards an adjacent on-top site to transiently occupy a metastable site, which is slightly displaced from the center of an on-top site through repulsive interaction with adjacent on-top CO molecules. Analysis of action spectra for the shuttling events reveals the C-O stretch frequency of the metastable CO. We also constructed a modified potential energy surface incorporating the intermolecular interaction, which reveals the underlying mechanism and provides a new way to experimentally determine detailed information on the energetics of the metastable state. TOC GRAPHICS

KEYWORDS Scanning Tunneling Microscopy; Intermolecular Interaction; Potential energy surface ; Single molecule spectroscopy; Carbon Monoxide


Page 3 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Traditional spectroscopic methods provide spatially-averaged information on collections of molecules from which the properties of individual molecules are indirectly inferred. This masks how a specific molecule is affected by its local environment. In catalysis, some local molecular configurations might favor one reaction pathway, while other configurations, which may exist only momentarily, would lead to an alternative pathway. There is thus a crucial need for probes that can determine not only the local stable configuration around a molecule, but also can access the properties of a molecule in a transient metastable state. The advent of techniques with single-molecule spatial resolution, such as scanning probe microscopy, now provides a new way to observe local inhomogeneity and its consequences, such as superstructureconfined molecular rotation1 and environment-dependent tautomerization.2 Artificial configurations can even be created through single-molecule manipulation to exploit repulsive intermolecular interactions to create a so-called “molecular cascade”.3 However, it is still largely unknown how such locally inhomogeneous intermolecular interactions affect the vibrational and other properties of a molecule. Here we report on the dynamics and properties of carbon monoxide (CO) adsorbed on the Pt(111) surface at high coverages by means of scanning tunneling microscopy-action spectroscopy (STM-AS).4,5 Intermolecular interactions stabilize CO adsorption at bridge sites creating a local structure in which CO can shuttle between the bridge site and a metastable on-top site in response to the injection of tunneling electrons. We have constructed an empirical potential energy surface (PES) to describe the shuttling motion using previously published parameters.6,7 Our investigation provides quantitative energetic information on the metastable state and also demonstrates how intermolecular interactions can induce and control the surface dynamics associated with a localized arrangement of molecules. In practical catalysis, reactions generally take place at elevated pressures and hence elevated coverages and it is thus important to understand molecular properties at structures such as domain boundaries between ordered phases as well as the nature of molecular motion at high coverages. Moreover, while information of this sort can sometimes be obtained theoretically, for example from density functional theory calculations, the PES 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

that we present has been constructed solely from experimental information. The conclusions thus reached provide a valuable experimental benchmark for judging the validity of any future theoretical treatments of the same phenomena.

Figure 1. Schematic representation of a (√3×2)rect-COB unit superimposed on an STM image (a) and the identical units observed at various surface coverages (b-e) and superimposed models (g-j) showing characteristic intermolecular distances (legend in (f)) inside the overlayer structures. (red dot : on top CO (COT), blue dot : bridge CO (COB), gray line : underlying Pt lattice. (b) θ = 0.16 ML, VS = 0.1 V, IT = 0.5 nA, (c) θ = 0.22 ML, VS = 0.1 V, IT = 0.5 nA, (d) θ = 0.33 ML, VS = 2 mV, IT = 2 nA, (e) θ = 0.46 ML, VS = 10 mV, IT = 0.5 nA. All scale bars are 1 nm.

It is well known that CO adsorbed on Pt(111) primarily occupies the on-top sites (T) and forms the (√3×√3)R30˚ overlayer structure (at θ close to 1/3 ML), and c(4×2)-2CO domains at higher θ values with bridge site (B) occupation.8–10 We have discovered by molecularly-resolved STM imaging that the CO adsorbed at the bridge site (COB) is always stabilized at the center of a (√3×2)rect-COB unit (Figure 1a and Figure S1) over a wide range of θ.11 Figure 1b shows a local (√3×2)rect-COB unit surrounded by randomly distributed on-top CO molecules (COT) (θ = 0.13 ML). The formation of the local (√3×2)rectCOB unit containing a COB at the center can be explained by the collision-induced indirect occupation


Page 4 of 17

Page 5 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


mechanism,12,13 in which an impinging CO induces top-to-bridge conversion of pre-adsorbed COT. At surface coverages of 0.2 to 0.38 ML, there are two different phases that are commonly observed for (√3×√3)R30˚ superstructures containing (√3×2)rect-COB units in the boundary spaces (Figures 1c-d). One is a (√3×√3)R30˚ island-phase with an inter-island distance of √7a0 (a0 is the Pt-Pt distance, 2.77 Å) that occasionally contains a few (√3×2)rect-COB units as shown in Figures 1c,h, while the other is a (√3×√3)R30˚ island-phase with an inter-island distance of 2a0 and contains (√3×2)rect-COB units as components of the superstructure (Figures 1d,i).11 An increase in the surface coverage (θ > 0.38 ML) induces a phase transition from (√3×√3)R30˚ to a c(4×2)-2CO domain, in which the (√3×2)rect-COB units are periodically arrayed (Figures 1e,j).

Figure 2. Sample bias voltage (VS)-dependent change of bridge CO. (a) STM image of a (√3×2)rectCOB unit at VS = 100 mV, and (b) STM image at the same position at VS = 230 mV, showing noise at the COB position (image size: 3 nm×3 nm) (c) representative current trace measured at the COB position with an open feedback loop, at VS = 227.5 mV, showing a two-step current change.

Figure 2a shows an STM image of a (√3×2)rect-COB unit obtained at a sample bias voltage (VS) of 100 mV. The STM image changes at a VS of 230 mV, where a fluctuation in the tunneling current was observed as streaky noise around the COB position in the (√3×2)rect-COB unit, as shown in Figure 2b.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

These noisy features arise from the inter-site conversion between B sites and the adjacent T sites along the [110] direction (Figure S2), in which the motion of COB is characterized by a distinct two-level current trace obtained by positioning the STM tip at the center of a (√3×2)rect-COB unit (VS = 227.5 mV) as shown in Figure 2c. To distinguish the confined T sites, we label them as T* to describe the shuttling behavior of the CO molecule as an inter-site conversion between B and T*. With this notation, the low and high-current levels in the current trace correspond to COB and CO on the T* sites (COT*) in the (√3×2)rect-COB unit, respectively.


Page 6 of 17

Page 7 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (a) Potential energy surface (PES) for a (√3×2)rect-COB unit (purple, C), obtained by summation of the PES at low coverage (black, A) and the lateral interaction potential (pink, B) in terms ] direction. (b) action spectra for both BT* (blue circles) and of displacement of COB along [ T*B (red rectangles). Over the entire range of VS, Iset = 0.34 nA at the COB marked in the inset image (VS = 100 mV and IT = 0.5 nA). Right-bottom inset: IT-dependent hopping rate for the reaction order N: N = 1 except for the T*B hopping at 240 mV (N = 0.7).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

In this B-T* shuttling motion, COT* is considered to be a metastable adsorption species that is less stable than COB, resulting in mutually exclusive site-switching dynamics upon the injection of tunneling electrons. The BT* hopping forms a local (1×1) arrangement among one COT* and two COT moieties11 leading to a repulsive intermolecular interaction, which is likely the origin of the destabilization of COT*.8 However, there has been no direct evidence of the existence or energetics of this metastable species. To explore the existence of COT* and the mechanism of B-T* shuttling, a modified PES was constructed (Figure 3a), and STM-AS was measured and analyzed for B-T* shuttling (Figure 3b). For the construction of the modified PES, the PES of an isolated CO (Fig. 3a, A) was first considered using the T-T diffusion barrier height ( )14–16, the difference in the adsorption energies between B and T,6,17 and the corresponding RC mode energies (ℏω)6,18 with simple truncated harmonic potentials at each adsorption site, as listed in Table 1. The contribution of the intermolecular interaction is expressed as a sum of pairwise lateral interaction potentials7 over the five CO molecules in a (√3×2)rect-COB unit, as a function of displacement (v) of COB along the [110] direction (Figure S3). The employed interaction potential Elat(r) is based on a short-range dipole-dipole interaction and a long-range oscillating interaction as a function of intermolecular distance (r), with empirically fitted parameters to reproduce experimentally observed overlayer structures.

=

−

! $! % ! # " $!

(1)

The resultant PES is shown in Figure 3a, C. The initial PES, which is of an infinitely repeating doublewell type, is transformed into a confined double-well type with two degenerate T* sites. Three characteristic features of T* are observed: (1) T* is less stable than B, (2) the position of the potential minimum of T* (v = 0.36 a0) is shifted from T (v = 0.5 a0), and (3) the intermolecular interaction stiffens the harmonic parabola for T* compared to that for T, indicating an increase in ℏω.6 Consequently, the modified PES clearly reveals the existence of metastable COT*, which is different from COT. Moreover,


Page 8 of 17

Page 9 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the energetic parameters of B-T* shuttling, i.e., 'over-barrier' type hopping dynamics,19 can be estimated from the PES, as discussed below in conjunction with the action spectra.

Table 1 Parameters for PES, estimated branching ratio and rate constants, and experimentally obtained parameters COT

COB

COT*

Internal stretch mode energy (ℏ&

260 meV a

230 meV a

252 meV e

RC mode energy (ℏ'

7 meV b

38 meV c

Anharmonic coupling constant ℏ('

0.25 meV c

5 meV c

Barrier height )

156 meV d

96 meV c,d

Branching ratio * = ,/,-.

1.2 × 10-24

2.0 × 10-5

Effective rate constant from (K=ηP)

1.2 × 10-25

2.0 × 10-6

Effective rate constant from the experiment, K

-

4.0 × 10-6 e

a

1.5 × 10-7 e

Ref 9; b Ref 18,20; c Ref 6; d Ref 14; e estimated from the action spectra (see Supporting Information)

We then measured the action spectra for B-T* shuttling (both BT* and T*B). The overall procedure for the STM-AS measurement was as follows. After measuring the current traces (Figures 2c) as a function of VS, the time (t) required for both the B to T* (BT*, from low to high-current level) and T*to B (T*B, from high to low-current level) hopping events were separately extracted. The hopping yield (Y(VS)) is 1/Ne, where Ne is the statistically estimated number of electrons for inducing a hopping event (Ne = t × IT / e) at each applied VS. For precise interpretation, Y(V) was then fitted with an empirical formula developed by Motobayashi et al. (Eq. 2), to extract the characteristic parameters. 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

01 = ∑4 34

56,89 ,:9 ;9 6

Page 10 of 17

(2)

where K is the effective rate constant, Ω is the vibrational mode energy (i.e., the threshold position in Y(V)), = is the vibrational broadening factor, and N is the reaction order. The measurement of power-law dependence of the hopping rate (R) on the applied IT (R ∝ITN) for the entire range of VS revealed that the value of N is unity (inset of Figure 3b).22 With the parameters Ω and K extracted from spectral fitting (Supporting information), the hopping dynamics of both BT* and T*B were determined and are discussed below. The value of Ω for COB (Ω) ) in the case of the BT* hopping was found to be 229 mV from the action spectrum (Fig. 3b), which coincides with the vibrational energy (230 meV) reported for the internal stretch (IS) mode of COB measured by infrared reflection-absorption spectroscopy23 and high-resolution electron energy loss spectroscopy.9 It has been reported that the lateral hopping motion of CO on Pd(110) is induced by the excitation of the IS mode with inelastically tunneled electrons from the STM tip. During this process, the vibrational energy of the IS mode is transferred to the low-energy RC mode via anharmonic coupling, to overcome the energy barrier for lateral hopping.4 In the present experiment, the mechanism of BT* hopping can be understood in the same manner. Persson and Ueba showed that the branching ratio (P) could be represented as the ratio of transition rate to the motion (w) to dissipation rate through electron-hole pair creation (weh) (Eq. 3).24 This is a characteristic parameter for describing an over-barrier process19 involving energy transfer between vibrational modes via anharmonic coupling.4 >

eh

G

D ℏ B EFℏH FK # ,I I J G CD F D #

*=> ≈

ℏH

C

D = ℏB (3)

In the above equation, ℏδω is the anharmonic coupling constant. According to the formal theory of Y(V), the order-of-magnitude of K with N = 1 can be estimated as 3 = M*, the product of the theoretically derived parameter P and the ratio of the number of inelastic electrons to the number of total injected 10 ACS Paragon Plus Environment

Page 11 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


electrons, M.24,25 Assuming 0.1 for M,21 the value of the experimentally obtained K (4.0 × 10-6) from the action spectrum for the BT* hopping and P (2.0 × 10-5) for COB estimated using the reported parameters (ℏδω, ) , and ℏω, see Table 1) are in reasonable agreement. It is noteworthy that the much smaller P value (10-24) for COT is due to the weak anharmonic coupling (ℏδω) as well as the large value of ϵ) /ℏω (Table 1) and accounts for the negligible hopping probability of COT by vibrational excitation, which is consistent with the results of our previous experiment.11 The metastable COT* can be investigated using parameters (ΩP∗ = 252 meV and KT* = 1.5×10-7 ) obtained from the action spectrum for T*B as shown in Fig. 3b. The first parameter, ΩP∗ (252 meV), which is the IS mode energy of metastable COT*, has never been measured with conventional spectroscopic methods. Interestingly, ΩP∗ appears to be significantly lower than the corresponding value for COT (260 ± 2 meV at various surface coverages and temperatures).23,26 We suggest that the difference in the energy of the IS modes of COT* and of COT is caused by the increased antibonding π*-orbital character in the electronic structure of COT*, which results from its off-center position with respect to the surface Pt atom (Figure 3a). This is consistent with the models describing the electronic structure of CO on various metals, where the increase in the π*-orbital character is correlated with the decrease of the C-O bond strength. As a result, the IS mode energy is decreased.27,28



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. (a-c) AS spectra obtained for the (√3×2)rect-COB units incorporated in three different superstructures. (d) model PES for describing the action spectra (a)-(c) (see Supporting Information for the estimate of the lateral interaction potential).

In addition to the dynamics of COB and metastable COT* confined in an isolated (√3×2)rect-COB unit, we have also examined the influence of the structures surrounding the (√3×2)rect-COB unit on the B-T* shuttling behavior. Figures 4a, b, and c are action spectra obtained from the (√3×2)rect-COB units incorporated into three different superstructures corresponding to Figures 1b, c, and d, respectively. All AS spectra shown in Figures 4a-c exhibit similar features for BT* hopping, with similar threshold energies (229 meV) and hopping yields. However, the T*B spectra are significantly different. In this case, the action spectrum from a (√3×2)rect-COB unit at a relatively low surface coverage (Figure 4a) shows an apparent threshold near the IS mode energy (252 meV), while the other two spectra with (√3×2)rect-COB units surrounded by extraneous CO superstructures at higher surface coverage (Figures 4b-c) do not show any threshold. In addition, the T*B hopping yield significantly increases with increase in the CO number density in the surrounding superstructures. Deeper understanding of this observation requires further modification of the corresponding PESs, as discussed below.


Page 12 of 17

Page 13 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


If the modified PES scheme in Figure 3 is considered, the intermolecular interaction contribution to the PES needs to include CO molecules outside the (√3×2)rect-COB unit. Figure 4d shows PESs constructed with corresponding models (see Figure S4 and text therein for the details), under the assumption of immobile COs except shuttling COB. The potential minima of the T* vertically shift upwards from a to c, resulting in reduction of ) for the T*B hopping ( ),P∗ R < ),P∗ T < ),P∗ U in Figure 4d). Moreover, an increase in lateral interaction stiffens the curve, indicating an increase in ℏω for COT* (ℏωP∗ R > ℏωP∗ T > ℏωP∗ U ). Accordingly, n in eq.(3) decreases (Table S2), which leads to an increase in the overall branching ratio, i.e. the yield of T*B hopping. In comparison, n in BT* hopping is less affected by surrounding superstructures, as indicated by the negligible change in both the AS and PES. Considering the mechanism of anharmonic mode coupling for vibrationally induced single-molecule dynamics, the first limiting condition is that the vibrational energy of the entrance mode (high-frequency mode) should exceed ) . A reduction in ) allows lower-frequency modes, such as the M-C stretch mode or a hindered rotational mode, to act as additional entrance modes, which causes the threshold to vanish at the IS mode energy (Figs. 4b-c).29 This indicates that the surrounding structures affect the dynamics of metastable COT*. To conclude, we have investigated the vibrationally induced shuttling of a COB molecule involving pseudo-excited metastable COT* in a confined configuration ((√3×2)rect-COB) by means of STM-AS, demonstrating how the local and inhomogeneous molecular arrangements affect the dynamics and vibrational properties of a single molecule. Particularly, the pseudo-excited metastable COT* exhibits a distinct internal stretch mode energy that was not measurable in previous studies with conventional spectroscopic methods that yield only spatially averaged information. These findings provide new insights into a model catalytic system at high surface coverages where intermolecular interactions become significant.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 17

EXPERIMENTAL All experiments were performed using a low-temperature scanning tunneling microscope (Scienta Omicron) in an ultra-high vacuum (UHV) chamber (PBase = 2.6 × 10-9 Pa). A Pt(111) single crystal surface was cleaned using several cycles of Ar ion sputtering (1.5 keV and 8 µA) and annealing (1100 K), followed by oxidation (1.0 × 10-5 Pa of O2, 800 K) and flashing at 1070 K. All data, such as the STM images and action spectra were collected at 4.7 K, using an electrochemically etched tungsten tip. CO molecules were adsorbed onto the Pt(111) surface through a dosing tube located near the surface at ~50 K. The surface coverage (θ) was estimated by counting the number of CO molecules in the STM images. The action spectra were obtained by repeated measurements of current-traces over a range of sample bias voltages, at a constant tunneling current.

ACKNOWLEDGEMENT This work was partially supported by a Grant-in-Aid for Scientific Research(S) “Single Molecule Spectroscopy using Probe Microscope” from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan and partially supported by the Global COE Program (Chemistry Innovation through Cooperation of Science and Engineering), MEXT, Japan. The authors sincerely thank Hiromu Ueba and Kenta Motobayashi, Jaehoon Jung and Miwa Kuniyuki for fruitful discussions and reading of the manuscript. H.J.Y. acknowledges the Junior Research Associate (JRA) program of RIKEN for support. M. T. acknowledges support from a grant from the US National Science Foundation (CHE1464816).

SUPPORTING INFORMATION


Page 15 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


STM images of COB (Figure S1) and temporarily captured COT* (Figure S2); detail of PES construction with intermolecular interaction energy according to the local molecular configurations; details of spectral fitting of the action spectra.

REFERENCES (1) Kühne, D.; Klappenberger, F.; Krenner, W.; Klyatskaya, S.; Ruben, M.; Barth, J. V. Rotational and Constitutional Dynamics of Caged Supramolecules. Proc. Natl. Acad. Sci. 2010, 107, 21332–21336. (2) Kumagai, T.; Hanke, F.; Gawinkowski, S.; Sharp, J.; Kotsis, K.; Waluk, J.; Persson, M.; Grill, L. Controlling Intramolecular Hydrogen Transfer in a Porphycene Molecule with Single Atoms or Molecules Located Nearby. Nat. Chem. 2014, 6, 41–46. (3)

Heinrich, A. J.; Lutz, C. P.; Gupta, J. A.; Eigler, D. M. Molecule Cascades. Science 2002, 298, 1381–1387.

(4) Komeda, T.; Kim, Y.; Kawai, M.; Persson, B. N. J.; Ueba, H. Lateral Hopping of Molecules Induced by Excitation of Internal Vibration Mode. Science 2002, 295, 2055–2058. (5) Kim, Y.; Motobayashi, K.; Frederiksen, T.; Ueba, H.; Kawai, M. Action Spectroscopy for Single-Molecule Reactions – Experiments and Theory. Prog. Surf. Sci. 2015, 90, 85–143. (6) Schweizer, E.; Persson, B. N. J.; Tüshaus, M.; Hoge, D.; Bradshaw, A. M. The Potential Energy Surface, Vibrational Phase Relaxation and the Order-Disorder Transition in the Adsorption System Pt{111}-CO. Surf. Sci. 1989, 213, 49–89. (7) Myshlyavtsev, A. V.; Stishenko, P. V. Potential of Lateral Interactions of CO on Pt (111) Fitted to Recent STM Images. Surf. Sci. 2015, 642, 51–57. (8) Ertl, G.; Neumann, M.; Streit, K. M. Chemisorption of CO on the Pt(111) Surface. Surf. Sci. 1977, 64, 393– 410. (9) Froitzheim, H.; Hopster, H.; Ibach, H.; Lehwald, S. Adsorption Sites of CO on Pt (111). Appl. Phys. 1977, 13, 147–151. (10) Steininger, H.; Lehwald, S.; Ibach, H. On the Adsorption of CO on Pt(111). Surf. Sci. 1982, 123, 264–282. (11) Yang, H. J.; Minato, T.; Kawai, M.; Kim, Y. STM Investigation of CO Ordering on Pt(111): From an Isolated Molecule to High-Coverage Superstructures. J. Phys. Chem. C 2013, 117, 16429–16437. 15 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 17

(12) Nekrylova, J. V.; Harrison, I. Site Resolved Adsorption Dynamics of CO on Pt(111). Chem. Phys. 1996, 205, 37–46. (13) Kawai, M.; Yoshinobu, J. Direct and Indirect Mechanisms in Site Occupation of CO Molecules on Ni(100) and Pt(111). Surf. Sci. 1996, 368, 239–246. (14) Nekrylova, J. V.; Harrison, I. Single Hop Diffusion of CO from Bridge to Top Sites on Pt(111). J. Chem. Phys. 1994, 101, 1730–1733. (15) Reutt-Robey, J. E.; Doren, D. J.; Chabal, Y. J.; Christman, S. B. Microscopic CO Diffusion on a Pt(111) Surface by Time-Resolved Infrared Spectroscopy. Phys. Rev. Lett. 1988, 61, 2778–2781. (16) Ma, J.; Xiao, X.; DiNardo, N. J.; Loy, M. M. T. Diffusion of CO on Pt(111) Studied by an Optical Diffraction Method. Phys. Rev. B 1998, 58, 4977–4983. (17) Mieher, W. D.; Whitman, L. J.; Ho, W. A Time Resolved Electron Energy Loss Spectroscopy Study of CO on Pt(111): Adsorption Site Occupations versus Coverage and Temperature. J. Chem. Phys. 1989, 91, 3228–3239. (18) Lahee, A. M.; Toennies, J. P.; Wöll, C. Low Energy Adsorbate Vibrational Modes Observed with Inelastic Helium Atom Scattering: CO on Pt(111). Surf. Sci. 1986, 177, 371–388. (19) Frederiksen, T.; Paulsson, M.; Ueba, H. Theory of Action Spectroscopy for Single-Molecule Reactions Induced by Vibrational Excitations with STM. Phys. Rev. B 2014, 89, 035427. (20) Graham, A. P. The Low-Frequency Vibrational Modes of c(4×2) CO on Pt(111). J. Chem. Phys. 1998, 109, 9583. (21) Motobayashi, K.; Kim, Y.; Ueba, H.; Kawai, M. Insight into Action Spectroscopy for Single Molecule Motion and Reactions through Inelastic Electron Tunneling. Phys. Rev. Lett. 2010, 105, 076101. (22) Kim, Y.; Komeda, T.; Kawai, M. Single-Molecule Reaction and Characterization by Vibrational Excitation. Phys. Rev. Lett. 2002, 89, 126104. (23) Hayden, B. E.; Bradshaw, A. M. The Adsorption of CO on Pt(111) Studied by Infrared ReflectionAbsorption Spectroscopy. Surf. Sci. 1983, 125, 787–802. (24) Persson, B. N. J.; Ueba, H. Theory of Inelastic Tunneling Induced Motion of Adsorbates on Metal Surfaces. Surf. Sci. 2002, 502-503, 18–25. (25) Ueba, H. Analysis of Lateral Hopping of a Single CO Molecule on Pd(110). Phys. Rev. B 2012, 86, 035440. (26) Tüshaus, M.; Schweizer, E.; Hollins, P.; Bradshaw, A. M. Yet Another Vibrational Study of the Adsorption System Pt{111}-CO. J. Electron Spectrosc. Relat. Phenom. 1987, 44, 305–316. (27) Blyholder, G. Molecular Orbital View of Chemisorbed Carbon Monoxide. J. Phys. Chem. 1964, 68, 2772– 2777. (28) Föhlisch, A.; Nyberg, M.; Bennich, P.; Triguero, L.; Hasselström, J.; Karis, O.; Pettersson, L. G. M.; Nilsson, A. The Bonding of CO to Metal Surfaces. J. Chem. Phys. 2000, 112, 1946–1958. 16 ACS Paragon Plus Environment

Page 17 of 17

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(29) Oh, J.; Lim, H.; Arafune, R.; Jung, J.; Kawai, M.; Kim, Y. Lateral Hopping of CO on Ag(110) by Multiple Overtone Excitation. Phys. Rev. Lett. 2016, 116, 056101.


Single-Molecule Dynamics in the Presence of Strong Intermolecular

Recommend Documents