Microwave, High-Resolution Infrared, and Quantum Chemical Investigations of CHBrF₂: Ground and v₄ = 1 States

Abstract

A combined microwave, infrared, and computational investigation of CHBrF(2) is reported. For the vibrational ground state, measurements in the millimeter- and sub-millimeter-wave regions for CH(79)BrF(2) and CH(81)BrF(2) provided rotational and centrifugal-distortion constants up to the sextic terms as well as the hyperfine parameters (quadrupole-coupling and spin-rotation interaction constants) of the bromine nucleus. The determination of the latter was made possible by recording of spectra at sub-Doppler resolution, achieved by means of the Lamb-dip technique, and supporting the spectra analysis by high-level quantum chemical calculations at the coupled-cluster level. In this context, the importance of relativistic effects, which are of the order of 6.5% and included in the present work using second-order direct perturbation theory, needs to be emphasized for accurate predictions of the bromine quadrupole-coupling constants. The infrared measurements focused on the ν(4) fundamental band of CH(79)BrF(2). Fourier transform investigations using a synchrotron radiation source provided the necessary resolution for the observation and analysis of the rotational structure. The spectroscopic parameters of the v(4) = 1 state were found to be close to those of the vibrational ground state, indicating that the ν(4) band is essentially unaffected by perturbations.

Rotational spectroscopy of imidazole: improved rest frequencies for astrophysical searches

“…Geometry optimisations and harmonic force-field data were performed using the CFOUR suite of programs 2 and its implementation of analytic second derivatives (Gauß & Stanton 1997), while to calculate the sextic centrifugal distortion constants, the VPT2 expressions (Aliev & Watson 1976 were adopted using an appropriate suite of programs (Pietropolli Charmet & Cornaton 2018). Nuclear quadrupole coupling constants for the nitrogen atoms were computed at the CCSD(T)/cc-pCVTZ level of theory and correlating all the electrons using the same procedure outlined in previous studies (Cazzoli et al 2011;Pietropolli Charmet et al 2016).…”

What are the spectroscopic properties of HFC-32? Answers from DFT

“…Thanks to the huge progresses made in computer hardware resources and the development of efficient algorithms, in the last years coupled cluster (CC) theory with singles, doubles excitations and a perturbative estimate of connected triples, CCSD(T), coupled to large basis sets or complete basis set extrapolation, has become the gold standard for the accurate prediction of thermochemical and spectroscopic properties of small molecules, containing up to a 10th of atoms (e.g., see Refs. [ and references therein). Nevertheless, due to the unfavorable scaling of CCSD(T) with system size ( N 6 – N 7 , N being the number of basis functions), the method cannot be routinely applied to medium and large systems which are of relevance in biochemistry, supramolecular chemistry, solid state chemistry, and material science.…”

Anharmonic resonances in the CH chromophore overtone spectra of CHBrF2

“…In this case, the relative intensities are computed employing the following weighted average [26]: (12) where b and a are the indexes of the chromophore states having v 1 = N -1/2, v 2 = 1, v 7 = 0 and v 1 = N -1/2, v 2 = 0, v 7 = 1, respectively. The weighting factor f is given by the experimental intensity ratio of the first two components of the N = 3/2 polyad:…”

“…In a first work [11] we have reported on the vibrational analysis of its infrared gas phase spectra in the 200 -9500 cm -1 region coupled to ab initio calculations and to the accurate determination of absorption cross sections. Subsequently, a combined microwave and high-resolution infrared study [12] supported by high-level quantum chemical computations has been carried out leading to accurate values of spectroscopic parameters for both the ground and the v 4 = 1 vibrational states.…”