Assignment of the vibrations of the S0, S1, and D0+ states of perhydrogenated and perdeuterated isotopologues of chlorobenzene

Vibrations of the p-chlorofluorobenzene cation

Vibrational wavenumbers are established for twenty modes of the p-chlorofluorbenzene cation and two Fermi resonances are identified in the S₁ state.

Vibration and vibration-torsion levels of the S1 state of para-fluorotoluene in the 580-830 cm-1 range: Interactions and coincidences

A study of the vibration and vibration-torsion levels of para-fluorotoluene in the 580-830 cm^-1 region is presented, where a number of features are located whose identity is complicated by interactions and overlap. We examine this region with a view to ascertaining the assignments of the bands; in particular, identifying those that arise from interactions involving various zero-order states (ZOSs) involving both vibrations and torsions. Resonance-enhanced multiphoton ionization (REMPI) is employed to identify the wavenumbers of the relevant transitions, and subsequently zero-kinetic-energy (ZEKE) spectra are recorded to assign the various eigenstates. In some cases, a set of ZEKE spectra are recorded across the wavenumber range of a REMPI feature, and we construct what we term a two-dimensional ZEKE (2D-ZEKE) spectrum, which allows the changing ZOS contributions to the eigenstates to be ascertained. Assignment of the observed bands is aided by quantum chemical calculations and all b₁ and a₂ symmetry vibrational wavenumbers are now determined in the S₁ state and cation, as well as those of the D₁₀ vibration. We also compare to the activity seen in the corresponding S₁ ← S₀ spectrum of para-difluorobenzene.

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

For the first time, a molecular symmetry group (MSG) analysis has been undertaken in the investigation of the electronic spectroscopy of p-xylene (p-dimethylbenzene). Torsional and vibration-torsional (vibtor) levels in the S₁ state and ground state of the cation of p-xylene are investigated using resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) spectroscopy. In the present work, we concentrate on the 0-350 cm^-1 region, where there are a number of torsional and vibtor bands and we discuss the assignment of this region. In Paper II [W. D. Tuttle et al., J. Chem. Phys. 146, 124309 (2017)], we examine the 350-600 cm^-1 region where vibtor levels are observed as part of a Fermi resonance. The similarity of much of the observed spectral activity to that in the related substituted benzenes, toluene and para-fluorotoluene, is striking, despite the different symmetries. The discussion necessitates a consideration of the MSG of p-xylene, which has been designated G₇₂, but we shall also designate [{3,3}]D_2h and we include the symmetry operations, character table, and direct product table for this. We also discuss the symmetries of the internal rotor (torsional) levels and the selection rules for the particular electronic transition of p-xylene investigated here.

Torsion and vibration-torsion levels of the S1 and ground cation electronic states of para-fluorotoluene

We investigate the low-energy transitions (0-570 cm^-1) of the S₁ state of para-fluorotoluene (pFT) using a combination of resonance-enhanced multiphoton ionization and zero-kinetic-energy (ZEKE) spectroscopy and quantum chemical calculations. By using various S₁ states as intermediate levels, we obtain ZEKE spectra. The differing activity observed allows detailed assignments to be made of both the cation and S₁ low-energy levels. The assignments are in line with the recently published work on toluene from the Lawrance group [J. R. Gascooke et al., J. Chem. Phys. 143, 044313 (2015)], which considered vibration-torsion coupling in depth for the S₁ state of toluene. In addition, we investigate whether two bands that occur in the range 390-420 cm^-1 are the result of a Fermi resonance; we present evidence for weak coupling between various vibrations and torsions that contribute to this region. This work has led to the identification of a number of misassignments in the literature, and these are corrected.