Supporting information for: Geometry

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1 Supporting information for: C Cl/Cu(4): Interaction and Adsorption Geometry Takamasa Makino, Siti Zulaehah, Jessiel Siaron Gueriba, Wilson Agerico Diño,,, and Michio Okada, Institute of Radiation Sciences and Department of Chemistry, Osaka University, Toyonaka, Osaka , Japan. Department of Applied Physics, Osaka University, Suita, Osaka , Japan. Center for Atomic and Molecular Technologies, Osaka University, Suita, Osaka , Japan. wilson@dyn.ap.eng.osaka-u.ac.jp; okada@chem.sci.osaka-u.ac.jp S1. Determination of the coverage Θ[ML] of C Cl on Cu(4) We determined the coverage Θ[ML] of C Cl on Cu(4) from TPD spectra as follows. We checked the pressure rise by the ionization gauge dosing C Cl. First, we calibrated the true pressure of C Cl (P C Cl) using the relative gauge gas correction factor for C Cl. Then, we converted the pressure of C Cl to the impingement rate of desorbed C Cl (Γ C Cl) into a quadrupole mass spectrometer (QMS). The impingement S1

2 rate of the molecule is generally described by the following equation: Γ = n ν 4, (1) where n is the number density of molecules, ν is the average speed of molecules. Using the ideal gas law, we can relate P C Cl to Γ C Cl as follows: Γ C Cl = P C Cl ν 4k B T, (2) where k B is the Boltzmann constant. Next, we related Γ C Cl to the signal of QMS at m/e = 50 (C Cl + ). We dosed various amounts of C Cl gas into the chamber and checked both the pressure rise by ionization gauge and the signal at m/e = 50 (C Cl + ) by the QMS. Using Eq. (2) and the relation between the pressure rise and QMS signal, we converted the QMS signal at m/e = 50 (C Cl + ) to Γ C Cl. Therefore, the TPD spectra can be represented as Γ C Cl vs. time curves. We integrated the TPD spectra and calculated the TPD area in units of molecules/cm 2. Considering natural abundance, we also took into account 7 Cl, in addition to 5 Cl. Note that the C Cl gas we used in the experiment contained 0% C 7 Cl (and 70% C 5 Cl). Finally, we converted the TPD area into the units of ML (1 ML corresponds to molecules/cm 2 on Cu(4)). S2. Fitting anti-absorption line shape in C- symmetric stretching of C Cl on Cu(4) We fitted the C- symmetric stretching peak of C Cl on Cu(4) at the exposure of 0.5L (0.06ML) in Fig. 5 (main text). We assumed that this peak has two components, a normal IR absorption component and an anti-absorption component. The change in the IR reflectance S2

3 ( R) of the former is usually described by the Lorentz function and that of the latter by R anti = 4Mn a (Ω 2 ω 2 ) 2 mncτ cos θ (Ω 2 ω 2 ) 2 + ( ω /τ), () 2 where ω is the frequency of the oscillating electric field, M is the mass of the adsorbate, n a is the number of adsorbates per unit area, m is the mass of the electron (9.1 1 kg), n is the number of conduction electrons per unit volume ( /cm for Cu), c is the speed of light ( cm/s), 1/τ is the damping rate due to excitation of electron-hole pairs, θ is the incidence angle of the IR light (80 ), and Ω is the resonance frequency. S1 We used the following formula in order to fit the C- symmetric stretching peak in Fig. 5 (main text), R = (A + Bω) + D (ω E) 2 + G + 4Mn [ a (Ω 2 ω 2 ) 2 ] 1. (4) mncτ cosθ (Ω 2 ω 2 ) 2 + ( ω /τ) 2 The fitting parameters are A, B, D, E, G, Ω, and τ. The first term on the right-hand side gives the background. The second and third terms correspond to the normal absorption and anti-absorption components, respectively. To perform the fit, we first calculate the reflectance, and then convert the results to absorbance. First, we analyzed the normal vibration of C Cl to determine M of the C- symmetric stretching because this vibrational mode is not just a vibration between C atom and atom. To analyze the normal vibration of C Cl, we used the method developed by E.B. Wilson. S2,S We assumed an Urey-Bradley field-type intramolecular potential S4 and used the force constants reported in Ref. S5. As the G and F matrix of C Cl molecule for A1 mode, assuming tetrahedral angles, we have G A1 = µ C + µ Cl 1 µ C 4 µ C r µ C µ 4 C + µ µ Cr 1 4 µ C r 1 4 µ Cr 1 ( 16 µ C + 2µ )r 2, (5) S

4 F A1 = a d e d b f e f c. (6) ere, ( ) a = K C Cl + s 2 0 t2 0 F Cl, (7) b = K C + ( ) s 2 1 t2 1 F Cl + 8 F, (8) c = 2{ 1 [ ( CCl + t 0 t 1 + s 0s 1 } ] ( )F Cl r r Cl + C + 2 ) 5 F r κ, (9) 2 d = ( s 0 s 1 + t 0t 1 ) F Cl, () e = 6 ( s 0 t 1 t 0s 1 ) r F Cl, (11) { } f = 1 ( s 1 t 0 t ) 1s 0 r Cl F Cl r F, (12) where s 0 = 1 ( r Cl + 1 ) q Cl r, (1) s 1 = 1 q Cl ( 1 r Cl + r ), (14) S4

5 t 0 = 2 2 r, (15) q Cl t 1 = 2 2 r Cl q Cl, (16) q Cl = r 2 + r2 Cl + 2 r r Cl (17) µ i (i = C, Cl, and ) is the reciprocal of the mass of the atom to which i refers, r Cl and r are the C-Cl and C- bond-lengths, respectively, q Cl is the distance between atom and Cl atom. K,, F, and κ are the stretching constants, bending constants, repulsive constants, and intramolecular tensions. We solved the eigenvalue equation, GF λe = 0, and analyzed the normal vibration of C Cl belonging to A1 mode. We obtained a value of kg for M of C- symmetric stretching. Furthermore, simply from the peak intensity in the IRAS spectra, we calibrated the ratio of C Cl corresponding to the antiabsorption peak (possibly Sa geometry, see article) and obtained a value of molecules/cm 2 for n a. We fitted the peak in the units of reflectance in the range of 2902 to 2941 cm 1. Fitting the peak, we convoluted Eq. (4) and the Gauss function with the full width at half maximum (FWM) of 4 cm 1 (spectral resolution). Then, we converted the IRAS peak into the units of absorbance. The eventual fitted curves are shown in Fig. 5 (main text). The best fitted τ is s. References (S1) Persson, B.; Volokitin, A. On the Origin of Anti-Absorption Resonances in Adsorbate Vibrational Spectroscopy. Chem. Phys. Lett. 1991, 185, (S2) Wilson Jr., E. B. Some Mathematical Methods for the Study of Molecular Vibrations. S5

6 J. Chem. Phys. 1941, 9, (S) Mizushima, S.; Shimanouchi, T. Infrared Absorption and Raman Effect (in Japanese); Kyoritsu Shuppan Co., Ltd., (S4) Urey,.; Bradley, C. The Vibrations of Pentatonic Tetrahedral Molecules. Phys. Rev. 191, 8, (S5) Nakagawa, I. Normal Vibration of 1, 2-Dichloroethane (in Japanese). Nippon Kagaku Zasshi 195, 74, S6