The Use of Multidimensional Franck−Condon Simulations to Assess Model Chemistries:  A Case Study on Phenol

Abstract

Multidimensional Franck-Condon simulations of the dispersed fluorescence spectra of phenol generated with geometries obtained from the highly correlated post-Hartree-Fock methods CASSCF, MRCI, and SACCI are presented. While the simulations based on CASSCF and MRCI optimized geometries are very similar to each other and fail to reproduce the experimentally measured intensities faithfully, the simulations obtained from SACCI optimized geometries are very close to the experimental spectra. The code developed for the multidimensional Franck-Condon simulations is described. It is shown that the integral storage problem common to the evaluation of multidimensional Franck-Condon integrals can be overcome by saving all quantities needed to disk. This strategy allows the code to run on computers with limited resources and is very well suited for application to molecules with a very large number of vibrational modes.

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of bromobenzene and its perdeuterated isotopologue: Assignment of the vibrations of the S0, S1, and D0+ states of bromobenzene and the S0 and D0+ states of iodobenzene

“…Finally, Klimusheva et al 15 reported values for M 7 , M 23 , M 24 , M 25 and M 27 that are in moderately good agreement with our calculated values, but we did not see any contributions from these vibrations in the present work, nor have they been reported by others.…”

Assignment of the vibrations of the S, S1, and D+ states of perhydrogenated and perdeuterated isotopologues of chlorobenzene

“…ClBz-h5 (Aldrich, 99.8% purity) or ClBz-d5 (Aldrich, 99 atom% D) vapour, each with the naturally-occurring ratio of 35 Cl: 37 Cl, was seeded in ~5 bar of argon carrier gas and the gaseous mixture was passed through a General Valve pulsed nozzle (750 μm, 10 Hz, opening time of 150 μs) to create a free jet expansion, and hence almost all transitions are from the ground state zero-point vibrational level. The focused, frequency-doubled output of the dye laser passed through a vacuum chamber where it perpendicularly intersected the free jet expansion between two biased electrical grids located in the extraction region of a time-offlight spectrometer.…”

“…10,11,12 It is noted that the experiments of Murakami et al 10 are two-photon excitation, followed by ionization, while the experiments by Anderson et al 11 and Walter et al 12 are one-photon excitation followed by ionization. The Ortiz group 13 have also employed high-resolution, one-photon excitation REMPI spectroscopy in a supersonic beam, to obtain photoionization spectra of the origin band of the S1 state of the 35 ClBz-h5 and 37 ClBz-h5 molecules at a rotational temperature of 1 K; this allowed them to determine the shift of the origin band between the 35/37 Cl isotopologues. They report a shift of 0.14 ± 0.02 cm -1 , which is within the resolution of the present work, and hence we do not expect to be able to discern this; however, shifts of vibrational bands can be larger, and this will be commented on later.…”

“…We employ one-colour REMPI spectroscopy to record rotationally-cold, vibrationallyresolved electronic spectra of the S1  S0 transition in ClBz-h5 and ClBz-d5, for each of their 35 Cl and 37 Cl isotopologues. The spectra are assigned using the observed experimental isotopic shifts, employing available previous experimental and theoretical results, and additionally quantum chemical calculations for all of the isotopologues, carried out in the present work.…”

“…The simplest types of monosubstituted benzenes are the monohalobenzenes. In the following, we shall abbreviate the titular molecule, chlorobenzene, as ClBz; in addition, we shall indicate the isotopologue with a presuperscript, 35 or 37, and/or a suffix -h5 or -d5 as appropriate, so that 37 ClBz-d5 represents the 37 Cl isotopologue of the perdeuterated chlorobenzene molecule, for example. We shall also frequently refer to fluorobenzene, which will be denoted FBz.…”