Critical influences on the rate of intramolecular vibrational redistribution: a comparative study of toluene, toluene-d₃and p-fluorotoluene

Abstract

The intramolecular vibrational redistribution (IVR) dynamics following the excitation of a mode in the first electronically excited states of toluene, toluene-d3 and p-fluorotoluene that has predominantly C-CH3 stretching character and an internal energy of ~1200 cm(-1) have been compared using picosecond time-resolved photoelectron imaging spectroscopy as a probe. Temporal changes in the intensities of spectral features in each molecule have enabled IVR lifetimes of 12, 15 and 50 ps, respectively, to be determined. Our measurements show that doorway states are critical in mediating the IVR dynamics in toluene and toluene-d3, and we deduce that these doorway states, which are assigned in the course of this work, are also instrumental in reducing the IVR lifetimes of these molecules relative to p-fluorotoluene.

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

“…We shall also provide some remarks on the different IVR regimes. As will be seen below, and also in recent previous work 1,10,18 there are regions of the toluene REMPI spectrum that have a number of vibrational features close together in wavenumber. As such, it is possible that these arise as a result of Fermi resonance (FR), whereby two so-called zero-order states (ZOSs) interact and form two new vibrational eigenstates.…”

“…As in our previous paper, 1 two-colour zero-kinetic-energy (ZEKE) spectra were also recorded via several of the observed levels in order both to aid assignment of the S 1 vibrations, and to investigate the previously reported loss of structure observed, particularly in the photoelectron spectra recorded via these levels. In a recent publication, 10 we reported the results of picosecond time-resolved slow electron velocity map imaging (tr-SEVI), investigating a Fermi resonance at ∼1190 cm −1 . The latter paper will be discussed further below when considering the results of the present paper; additionally, further tr-SEVI results are presented for other features observed in the S 1 ← S 0 REMPI spectra.…”

“…Concentrating initially on the Tol-h 8 highest wavenumber, features are constituted predominantly of combinations of each of the ∼460 cm −1 FR components with M 10 . These values suggest that the intense bands U, V, and W at 1183.4, 1191.8, and 1196.2 cm −1 might be associated with the ∼460 cm −1 FR components in combination with eigenstate M, with the ∼460 cm −1 FR components in combination with eigenstate N appearing on the high wavenumber side to these features.…”

Molecular symmetry group analysis of the low-wavenumber torsions and vibration-torsions in the S1 state and ground state cation of p-xylene: An investigation using resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) spectroscopy

“…In particular, the assignment of the vibrations (atomic motion) will underpin models of how interactions with torsional motion occurs. In previous work, our group has also studied the pFT molecule; 4,12,13 as has the group of Lawrance, 14,15 some of which was in collaboration with ourselves. In addition, we shall make passing comment on previous fluorescence work on pFT, 16,17,18 ZEKE spectroscopy on toluene by Lu et al 19 and ZEKE spectroscopy on pFT by Takazawa et al 20 and ourselves.…”

“…2 and other work by the same group), with whom we have collaborated. 3,4 In previous work, our group has studied toluene, using resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) spectroscopy, 5,6 as has the group of Lawrance, 7 using two-dimensional laser-induced fluorescence (2D-LIF). Recently, this work was furthered by Lawrance and coworkers, 8,9 with the role of methyl groups in coupling to vibrational levels being emphasised.…”