Combined high resolution infrared and microwave study of bromochlorofluoromethane

Abstract

We report a detailed spectroscopic investigation of the chiral molecule bromochlorofluoromethane (CHBrClF) with rotational resolution using a pulsed nozzle beam Fourier transform microwave (FTMW) and a waveguide FTMW spectrometer as well as a supersonic jet interferometric Fourier transform infrared (FTIR) and infrared diode laser spectrometer. The rotational spectrum of CHBrClF has been measured between 8 and 18 GHz. The quadrupole hyperfine components have been fully resolved for the assigned rotational transitions with J⩽18. Three ground state rotational constants, five centrifugal distortion constants, and all five independent elements of the bromine and chlorine quadrupole coupling tensors have been determined for each of the four isotopomers CH79Br35CIF, CH81Br35CIF, CH79Br37CIF, and CH81Br37CIF from about 500 measured transition frequencies of the hyperfine components. The quadrupole coupling tensor has been transformed to its principal axes. The determinable sign combinations of the off-diagonal elements of the coupling tensor have been evaluated. Rotational transitions involving high J were measured by FTIR spectroscopy between 15 and 40 cm−1 (450–1200 GHz) using a light pipe cell, providing an estimate of the permanent dipole moment |μ|=(1.5±0.3) D from intensities. In the midinfrared, we have fully analyzed the rovibrational line structure of supersonic jet spectra of the CF-stretching fundamental ν4, giving band centers for the isotopomers CH79Br35CIF [ν̃ 40=1077.178 43(4) cm−1], CH81Br35CIF [ν̃=1077.133 06(4) cm−1], CH79Br37CIF [ν̃ 40=1076.7914(4) cm−1], and CH81Br37CIF [ν̃ 40=1076.730 26(5) cm−1]. A combined analysis of about 20 microwave frequencies, more than 100 infrared ground state combination differences, and about 70 infrared transition frequencies for each of the35Cl isotopomers finally provide accurate ground and excited state rotational parameters as well as structural parameters, which may be compared to ab initio calculations. The results are discussed in relation to the molecular structure as well as coincidences of ν4 absorptions with CO2 laser lines in view of CO2–laser pumping and possible spectroscopic studies of this chiral molecule at ultrahigh resolution.

Molecular chirality and the fundamental symmetries of physics: Influence of parity violation on rovibrational frequencies and thermodynamic properties

“…A first breakthrough was achieved with high-resolution molecular beam (supersonic jet) infrared diode laser and Fourier Transform Infrared Spectroscopy (FTIR), 30 which in an essential collaboration of the ETH Zürich microwave and infrared groups led to the first full high-resolution rotational analysis of the 1 CF-stretching fundamental. 26 In parallel with our studies of fluorooxirane 61 and dideuteroethyleneepisulfoxide, 62 this constituted the very first highresolution analysis of an infrared spectral band of any chiral molecule. While this late achievement may appear surprising to nonspectroscopists, it must be pointed out that chiral molecules by necessity have some minimum complexity and high-resolution IR spectra of such complexity were generally considered nonanalyzable by traditional techniques.…”

“…58 We may complement this "chemical" review by the recent successful gas chromatic separations 30,59,60 and improved synthesis techniques allowing for the production of large quantities of both the H and D isotopomers, 30,59,60 which were of importance for molecular beam spectroscopic studies in our group. 26 The infrared spectroscopy of CHBrClF has been of interest in relation to parity violation since the early unsuccessful IR-spectroscopic attempts by the group of Letokhov. 10,27,28 Experimental and theoretical efforts on this molecule in our own group started about a decade ago.…”

“…In addition to the effects mentioned, the symmetry violation leads in principle to observable differences of enantiomers in all relevant spectral ranges, be it NMR, 25 microwave, 26 infrared, [26][27][28][29][30][31] and generally optical as well as Mö␤bauer spectra. 32,33 In the literature cited, various proposals or actual attempts have been made to observe molecular parity violation; so far, all either unsuccessful or at best doubtful.…”

An experimental and theoretical study of the valence shell photoelectron spectrum of bromochlorofluoromethane

“…Bromochlorofluoromethane is one of the simplest chiral molecules possessing an asymmetric carbon atom and, as such, its geometric and electronic structure have attracted considerable interest [1][2][3][4][5][6]. Although the molecule contains two relatively heavy atoms, its size is sufficiently small for its physical properties to be calculated reliably using advanced theoretical and computational approaches.…”

Measuring molecular parity nonconservation using nuclear-magnetic-resonance spectroscopy

“…One method is to compare transition frequencies in the spectra of chiral enantiomers, and this has been attempted with microwave, infrared, and Mössbauer spectroscopy [5][6][7][8][9]. Other recently explored methods are to observe time-dependent optical activity in chiral molecules [10,11], or using Stark interference techniques in diatomic molecules [12,13].…”