The 700-1500 cm−1 region of the S1 ($\widetilde A{}^1B_2$Ã1B2) state of toluene studied with resonance-enhanced multiphoton ionization (REMPI), zero-kinetic-energy (ZEKE) spectroscopy, and time-resolved slow-electron velocity-map imaging (tr-SEVI) spectroscopy

Abstract

We report (nanosecond) resonance-enhanced multiphoton ionization (REMPI), (nanosecond) zero-kinetic-energy (ZEKE) and (picosecond) time-resolved slow-electron velocity map imaging (tr-SEVI) spectra of fully hydrogenated toluene (Tol-h8) and the deuterated-methyl group isotopologue (α3-Tol-d3). Vibrational assignments are made making use of the activity observed in the ZEKE and tr-SEVI spectra, together with the results from quantum chemical and previous experimental results. Here, we examine the 700–1500 cm−1 region of the REMPI spectrum, extending our previous work on the region ≤700 cm−1. We provide assignments for the majority of the S1 and cation bands observed, and in particular we gain insight regarding a number of regions where vibrations are coupled via Fermi resonance. We also gain insight into intramolecular vibrational redistribution in this molecule.

Vibrations of the S1 state of fluorobenzene-h5 and fluorobenzene-d5 via resonance-enhanced multiphoton ionization (REMPI) spectroscopy

“…It is straightforward to assign the band at 662.2 cm −1 , which was assigned as M 19 2 by Butler et al; 17 we agree, however, with Pugliesi et al 6 that the corresponding fundamental vibration is better described as a mixture of the S 0 M 18 and M 19 modes, and so we have designated this fundamental as M (18/19) when dispersing the fluorescence from each feature. 17 This is very similar to the behaviour observed for toluene and toluened 3 via dispersed fluorescence 22 and ZEKE spectroscopy, 20 where the same two vibrations are also in Fermi resonance.…”

“…To assign the FBz-d 5 spectrum, we first note that we expect to see similar vibrational activity in the spectrum of each of the two isotopologues since the change in the equilibrium geometry is the same; however, there will be differences in activity caused by vibrational effects, including vibrations undergoing isotopic shifts, and therefore moving in and out of Fermi resonance with each other. To aid the assignment, we have calculated the vibrational wavenumbers for the S 1 state of FBz-d 5 and present these values in Table IV 17 this is also in line with the conclusions reached for toluene, 20,22 where these vibrations are also in Fermi resonance. The calculated wavenumber suggests that M 10 d is providing the intensity for the features in Region α-see Figures 6 and 7.…”

“…We note that in our recent work on toluene, 10,20 we found that these scaled harmonic values were at least as reliable as the explicitly calculated anharmonic values (with the latter being very expensive to calculate). The S 0 vibrational modes of FBz-h 5 have been labelled as described in Ref.…”

“…In future work, as we have previously undertaken for para-fluorotoluene 25 and toluene, 10,20 we hope to undertake ZEKE spectroscopic studies to confirm some of the less secure assignments. We also intend to perform standard and twodimensional dispersed fluorescence experiments and the results of these will be complementary to the ZEKE ones.…”

Quantitative first principles calculations of protein circular dichroism in the near-ultraviolet

“…However, it is difficult to distinguish all the bands from various electronic transitions. For the purposes of our protein CD calculations, the origins of the 1 L b and 1 L a bands are placed at 290.5 and 285 nm, respectively, in accordance with the experimental measurements of tryptophan derivatives 45 and account for the energy shift induced by the surrounding residues or solvent. The Franck–Condon integrals for both states are shown in Table 3 .…”