Vibrations of the p-chlorofluorobenzene cation

Abstract

The vibrations of the ground state cation (X[combining tilde]2B1) of para-chlorofluorobenzene (pClFB) have been investigated using zero-electron-kinetic-energy (ZEKE) spectroscopy. ZEKE spectra were recorded using different vibrational levels of the S1 state as intermediate levels, for which assignments were put forward in an earlier paper [W. D. Tuttle, A. M. Gardner, and T. G. Wright, Chem. Phys. Lett., 2017, 684, 339]. These different intermediate levels dramatically modify the Franck-Condon factors for the ionization step. The adiabatic ionization energy (AIE) for pClFB was measured as 72 919 ± 5 cm-1, and analysis of the vibrational structure in the ZEKE spectra allowed further interrogation of the assignments of the REMPI spectrum. Assignment of the vibrational structure has been achieved by comparison with corresponding spectra of related molecules, via quantum chemical calculations, and via shifts in bands between the spectra of the 35Cl and 37Cl isotopologues. In this way it was possible to assign twenty out of the thirty vibrational modes of the ground state pClFB+ cation. Additionally, evidence for Fermi resonances between some vibrational levels was found in the S1 state, but no large-scale intramolecular vibrational redistribution (IVR) was seen in the spectra here. Finally, we discuss trends in AIE shifts for benzenes with one or two halogen atoms or methyl substituents.

Experimental and theoretical study on p-chlorofluorobenzene in the S, S1 and D states

“…6, it can be inferred from the vertical intercept that the AIP is 72937±8 cm −1 ((9.0428±0.0010) eV). The measured value agrees fairly well with the previously reported one [23]. agree with previously reported values of 373, 782, 821 and 1176 cm −1 , which are allocated to modes 7b 1 , 10a 1 , 10b 1 and 18a 1 .…”

“…The adiabatic ionization potential (AIP) of p-ClFPh was 9.011±0.008 eV, which was reported through the equilibrium measurement method in 1978 [22]. In addition, Kemp et al reported AIP of p-ClFPh as 9.0408±0.0006 eV and analyzed the vibrational structures in ZEKE spectra [23]. In the same year, our group reported the vibrations of meta-bromofluorobenzene in the first excited state (S 1 ) and the cationic ground state (D 0 ), also gave the adiabatic excited-state energy and AIP [24].…”

Unravelling overlaps and torsion-facilitated coupling using two-dimensional laser-induced fluorescence

“…The 2D-LIF and DF spectra show evidence of weak cross activity between 11 1 and 14 2 , but this could simply be FC activity. We have previously concluded that these levels are close to coincident in the pClFB molecule, 46 but that there was no clear evidence of interaction from the ZEKE spectra reported therein. In pFT, we have seen herein that there is also little evidence for any significant interaction between these two levels, which is in agreement with the results of our ZEKE study.…”

“…As a consequence, we conclude that each of the three states, 11 1 , 29 1 and 14 2 are inherently 'bright', again in agreement with conclusions we have made in other work on pFT and related molecules. 8,15,33,46 We have previously discussed in depth 29 a feature that appears at S1+845 cm -1 and the interactions there were isolated to the 18 2 m 1 level, which allowed couplings to vibtor combinations involving m = 2. In so-doing, the mechanism opens up couplings between vibrations of different symmetry; such is also included in the vibtor coupling of the three lowest-wavenumber vibrations included in the model of GL.…”

Detailed analysis of the vibronic structure of phenetole in its first excited state and ionic ground state

“…significant FC factor and all other observed vibrations gain intensity from that vibration. [59][60][61][62] Hence, the high intensity of, for example, the vibration 18b 1 in the MATI spectrum via 6b 1 (this work: 6a 1 ) of anisole has to be a result of either a simultaneous excitation or a mixed vibration in the S 1 state.…”