High resolution FTIR and diode laser spectroscopy of trifluoromethylacetylene and tetrafluoromethane in a supersonic jet expansion

Abstract

We report high resolution infrared spectra in the CF stretching fundamental ranges of trifluoromethylacetylene (CFC≡C-H, 3,3,3-trifluoropropyne) and of tetrafluoromethane (CF, R14, PCF-14, Halocarbon14). For the experiments a diode laser setup combined with a supersonic jet expansion is described, achieving approximate rotational temperatures between 5 and 10 K for CF, using a pulsed slit nozzle providing effective optical path lengths of 3 to 4 cm in a single pass. Slightly higher rotational temperatures (near 30 K) for CFCCH greatly simplify the rotational-vibrational structure of the spectra for this molecule, for which we report also high resolution Fourier transform (FTIR) spectra at room temperature with nearly Doppler limited resolution (instrumental bandwidth 0.001 cm) using the Zürich prototype spectrometer ZP 2001 (Bruker IFS125). The analysis of the CF-symmetric stretching (A) fundamental provides accurate spectroscopic parameters of the ground and excited vibrational states with a band centre = (1253.4985 ± 0.0015) cm from a least squares adjustment to more than 1100 line data with a root mean square deviation less than 0.0003 cm. The low temperature spectra of the degenerate (F) fundamental of CF show a very simple structure of line clusters which can be analysed with an approximate term formula. The spectra are essentially instrument limited with a smallest effective line width near 0.002 cm. The assignment of the P(1) line at 1283.33693 cm in the supersonic jet spectra (about 10 K) provides a band centre in terms of the vibrational energy of the ( = 1, J = 0, F (F)) level at (1283.7193 ± 0.002) cm. Also the assignment of the isolated R(0) line at 1283.48420 cm provides the energy of the well defined ( = 1, J' = 1, A (A)) level. The results are discussed in relation to the data from the HITRAN tables, earlier FTIR data, and new frequency comb based data for CF. We also discuss possible studies of nuclear spin symmetry conservation in CF, for which lower temperatures would be required, and a concept to study parity violation in CF by a level crossing experiment using molecular beam spectroscopy.