COMBINED HIGH-RESOLUTION INFRARED AND MICROWAVE STUDY OF BROMOCHLOROFLUOROMETHANE

We report a detailed spectroscopic investigation of the chiral molecul e bromochlorofluoromethane (CHBrClF) with rotational resolution using a pulsed nozzle beam Fourier transform microwave (FTMW) and a waveguid e FTMW spectrometer as well as a supersonic jet interferometric Fourie r transform infrared (FTMW) 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 as-signed rotational transitions with J less than or equal to 18. Thr ee ground slate relational constants, five centrifugal distortion cons tants, and all five independent elements of the bromine and chlorine q uadrupole coupling tensors have been determined for each of the four i sotopomers (CHBrCIF)-Br-79-C-35, (CHBrCIF)-Br-81-C-35, (CHBrCIF)-Br-79 -C-37, and (CHBrCIF)-Br-81-C-37 from about 500 measured transition fre quencies of the hyperfine components. The quadrupole coupling tensor h as been transformed to its principal axes. The determinable sign combi nations of the off-diagonal elements of the coupling tensor have been evaluated. Rotational transitions involving high J were measured by FT IR spectroscopy between 15 and 40 cm(-1) (450-1200 GHz) using a light pipe cell, providing an estimate of the permanent dipole moment \mu\=( 1.5+/-0.3) D from intensities. In the midinfrared, we have fully analy zed the rovibrational line structure of supersonic jet spectra of the CF-stretching fundamental nu(4), giving band centers for the isotopome rs (CHBrCIF)-Br-79-C-35 [<(nu)over tilde(4)(0)>=1077.178 43(4) cm(-1)] , (CHBrCIF)-Br-81-C-35 [<(nu)over tilde(4)(0)>=1077.133 06(4) cm(-1)], (CHBrCIF)-Br-79-C-37 [<(nu)over tilde(4)(0)>=1076.7914(4) cm(-1)], an d (CHBrCIF)-Br-81-C-37 [<(nu)over tilde(4)(0)>=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 t ransition frequencies for each of the Cl-35 isotopomers finally provid e accurate ground and excited state rotational parameters as well as s tructural parameters, which may be compared to nb initio calculations. The results are discussed in relation to the molecular structure as w ell as coincidences of nu(4) absorptions with CO2 laser lines in view of CO2-laser pumping and possible spectroscopic studies of this chiral molecule at ultrahigh resolution. (C) 1997 American Institute of Phys ics.