Tunable Diode Laser Spectroscopy of cis-1,2-Difluoroethylene:  Rovibrational Analysis of the ν₉ and ν₅+ν₁₀ Bands and Anharmonic Force Field

Abstract

cis-1,2-Difluoroethylene was synthesized, and the gas-phase infrared spectrum was investigated in the ν9 and ν5+ν10 band region (1350−1391 cm-1), at a resolution of about 0.002 cm-1, employing a tunable diode laser spectrometer. These vibrations of symmetry species B1 yield strong a-type bands. Most of the J and K structure was recorded in different subbranches and the rovibrational analysis led to the assignment of 2313 (J ≤ 64, K a ≤ 26) and 1172 (J ≤ 57, K a ≤ 20) transitions of the ν9 and ν5+ν10 bands, respectively. Using Watson's A-reduction Hamiltonian in the Ir representation a set of accurate spectroscopic parameters, up to four sextic centrifugal distortion terms, was obtained for both the excited states v 9 = 1 and v 5 = v 10 = 1. A Fermi resonance coupling constant W = 4.2(5) cm-1 was estimated for the perturbation between the ν9 and ν5+ν10 levels. Correlated harmonic force constants were obtained from coupled cluster CCSD(T) calculations with the cc-pVTZ basis set while the anharmonic force constants were computed at MP2 level using the same basis set. There is a good agreement with the available experimental data, in particular the equilibrium geometry compared with the experimental r 0 structure and the fundamental modes. In addition, the ab initio anharmonic force field of cis-1,2-difluoroethylene provided a critical assessment of the experimental spectroscopic parameters, especially in the treatments of strong Fermi interactions.

Accurate Vibrational–Rotational Parameters and Infrared Intensities of 1-Bromo-1-fluoroethene: A Joint Experimental Analysis and Ab Initio Study

“…Br isotopologue splittings being larger than 0.5 cm −1 ; see Tables 3 and 4). As also observed in other studies, 31,99,100 because of the inclusion of the off-diagonal interaction terms in the calculations of the TED (see expressions 30−32 of ref 99), for some normal modes the contribution due to a particular symmetry-adapted coordinate exceeds 100%.…”

“…Concerning normal modes ω 7 and ω 8 , the TED analysis leads to the description of both of them as combinations of symmetric coordinates also involving C–Br stretching; this is in agreement with the ab initio harmonic calculations that predict significantly different values for these modes (with the 79/81 Br isotopologue splittings being larger than 0.5 cm –1 ; see Tables and ). As also observed in other studies, ,, because of the inclusion of the off-diagonal interaction terms in the calculations of the TED (see expressions 30–32 of ref ), for some normal modes the contribution due to a particular symmetry-adapted coordinate exceeds 100%.…”

Study of the Vibrational Spectra and Absorption Cross Sections of 1-Chloro-1-fluoroethene by a Joint Experimental and Ab Initio Approach

“…Being considered trace gas pollutants, the kinetics of their reactions with O­( 3 P), and their photochemistry , and adsorption − on substrates suitable for subsequent photodegradation have also been investigated. For supporting the monitoring by means of spectroscopic techniques studies dealing with the computation of the vibrational frequencies, the analysis of resonances and determination of anharmonic constants from the assignments of low-resolution infrared spectra have been carried out for some halogenated ethenes. − …”