Abstract
We investigate Duschinsky rotation/mixing between three vibrations for both m-fluorotoluene (mFT) and m-chlorotoluene (mClT), during electronic excitation and ionization. In the case of mFT, we investigate both the S1 → S0 electronic transition and the D0 + ← S1 ionization, by two-dimensional laser-induced fluorescence (2D-LIF) and zero-electron-kinetic energy (ZEKE) spectroscopy, respectively; for mClT, only the D0 + ← S1 ionization was investigated, by ZEKE spectroscopy. The Duschinsky mixings are different in the two molecules, owing to shifts in vibrational wavenumber and variations in the form of the fundamental vibrations between the different electronic states. There is a very unusual behavior for two of the mFT vibrations, where apparently different conclusions for the identity of two S1 vibrations arise from the 2D-LIF and ZEKE spectra. We compare the experimental observations to the calculated Duschinsky matrices, finding that these successfully pick up the key geometric changes associated with each electronic transition and so are successful in qualitatively explaining the vibrational activity in the spectra. Experimental values for a number of vibrations across the S0, S1, and D0 + states are reported and found to compare well to those calculated. Assignments are made for the observed vibration-torsion ("vibtor") bands, and the effect of vibrational motion on the torsional potential is briefly discussed.
Highlights
An analysis of the vibrational activity in electronic and photoelectron spectra is often used as a signature of vibrational coupling between fundamentals, overtones, and combination levels
We focus on a set of three vibrations that are active in the S1 S0 transition, and are found to have a high degree of cross-activity, as ascertained using 2D-laser-induced fluorescence (LIF) and zero-electron-kinetic energy (ZEKE) spectroscopy
We look at the activity in the 2D-LIF and ZEKE spectra in more detail
Summary
An analysis of the vibrational activity in electronic and photoelectron spectra is often used as a signature of vibrational coupling between fundamentals, overtones, and combination levels This occurs through anharmonic coupling, which leads to the dispersal, and so delocalization, of internal energy within a molecule – an important aspect to enhancing photostability.[1,2,3,4] Sometimes activity in fundamentals other than that excited can be seen in experimental spectra; to first order, vibrational fundamentals do not couple anharmonically. Both Franck-Condon (FC) and Duschinsky effects will operate simultaneously, which can complicate the interpretation of the spectra
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
