Affiliation:
1. Department of Physics and Astronomy, University College London, London WC1E 6BT, UK
2. E.A. Milne Centre for Astrophysics, University of Hull, Hull HU6 7RX, UK
Abstract
ABSTRACT
We present a hybrid CCSD(T) + PBE-D3 approach to calculating the vibrational signatures for gas-phase benzene and benzene adsorbed on an ordered water ice surface. We compare the results of our method against experimentally recorded spectra and calculations performed using PBE-D3-only approaches (harmonic and anharmonic). Calculations use a proton ordered XIh water ice surface consisting of 288 water molecules, and results are compared against experimental spectra recorded for an ASW ice surface. We show the importance of including a water ice surface into spectroscopic calculations, owing to the resulting differences in vibrational modes, frequencies, and intensities of transitions seen in the IR spectrum. The overall intensity pattern shifts from a dominating ν11 band in the gas-phase to several high-intensity carriers for an IR spectrum of adsorbed benzene. When used for adsorbed benzene, the hybrid approach presented here achieves an RMSD for IR active modes of 21 cm−1, compared to 72 cm−1 and 49 cm−1 for the anharmonic and harmonic PBE-D3 approaches, respectively. Our hybrid model for gaseous benzene also achieves the best results when compared to experiment, with an RMSD for IR active modes of 24 cm−1, compared to 55 cm−1 and 31 cm−1 for the anharmonic and harmonic PBE-D3 approaches, respectively. To facilitate assignment, we generate and provide a correspondence graph between the normal modes of the gaseous and adsorbed benzene molecules. Finally, we calculate the frequency shifts, Δν, of adsorbed benzene relative to its gas-phase to highlight the effects of surface interactions on vibrational bands and evaluate the suitability of our chosen dispersion-corrected density functional theory.
Publisher
Oxford University Press (OUP)
Subject
Space and Planetary Science,Astronomy and Astrophysics