Vibrational C–H overtone spectroscopy and bond distances of butenes dissolved in liquid Xe

A VPT2 Route to Near-Infrared Spectroscopy: The Role of Mechanical and Electrical Anharmonicity

“…Calculations were also performed with the polarizable continuum model (PCM) through its integral equation formalism version (IEF-PCM) , to simulate the solvent effects (xenon). However, as expected and previously noted in ref , those effects are negligible.…”

“…As for naphthalene, it is interesting to start with a more technical discussion on the actual calculation of the transition moments, in connection with the problem of resonances. The symmetric and antisymmetric CH stretchings of CH 2 (noted CH o for the olefin CH vibrations in ref ) are well separated in energy with a shift of about 80 cm –1 . This is not the case for those of the methyl group (CH ip for the vibrations where the largest displacements are in the CCC planes and CH op for those out-of-plane, respectively modes 2 and 23 and 11 and 16 here), with about 2 cm –1 of difference between the symmetric and antisymmetric modes.…”

“…The transitions have been divided on the basis of the total number of quanta in the final state. The experimental spectra were taken from refs (left panel) and (right panel) and scaled so that its highest peak matched the highest theoretical one. The latter was shifted by +150 cm –1 .…”

“…The analysis of overtone spectra is then generally based on the local mode approach (see ref for a discussion on the underlying theory), where empirical parameters are used to evaluate the anharmonic contributions and interpret the observed spectra. The study of C–H stretchings can be facilitated by choosing well suited molecules, which explains the extensive study of alkenes and alkanes. − As a result, a large quantity of reference data has been collected and can be used for a preliminary validation of the procedure presented here. It should be noted that for CH stretchings, the energy levels at the VPT2 level are equivalent to those of the Morse potential, so it is expected that the perturbative approach remains accurate also for higher overtones .…”

“…The NIR spectrum of isobutene, or 2-methylpropene (Figure ), starting from the second overtone C–H stretching region has been recently recorded and analyzed with a local mode model . Following the same protocol as for the previous systems, the computed harmonic and anharmonic fundamental wavenumbers are reported in Table together with their experimental counterparts.…”