MICROWAVE SPECTRA AND ELECTRIC DIPOLE MOMENTS FOR LOW-J LEVELS OF INTERSTELLAR TRANSIENT AND RADICAL SPECIES

Author Institution: Molecular Physics Division, National Institute of Standards and Technology; Faculty of Liberal Arts, Shizuoka University; Department of Astrophysics, Nagoya UniversityA number of low-J rotational transitions have been measured for the radical and transient molecular species; SO, $C_{2}S$, $C_{3}S$, c-$HC_{3}$, $CH_{2}CC$, and c-$C_{3}$$H_{2}$ using a pulsed-nozzle Fabry-Perot-cavity Fourier transform microwave spectometer which employed a DC voltage electric discharge nozzle. Helmholtz coils around the outside of the vacuum chamber were used to maintain the magnetic field within the active volume element of the Fabry-Perot cavity to less than ten milliGauss. The transition frequencies measured are accurate in most instances to four kilohertz, thus allowing the molecular dynamics of cold interstellar clouds to be determined with improved accuracy. In addition, the molecular electric dipole moments have been determined for $SO, C_{3}S, c-HC_{3}$, and $c-C_{3}H_{2}$ from Stark-effect measurements and yield the following values: 1.52(2), 2.81(7), 2.30(1), and 3.27(1) Debye, respectively. The measurement of the spectra and Stark effect of several other radicals is in progress. The HCCN radical with $^{3}\Sigma$ ground state is being studied in collaboration wit Y. Ohshima and Y. Endo. The hyperfine structure of the $N_{K-, K+} = 1_{0, 1} - 0_{0,0}$ transition of $CH_{2}CN$ has been observed in collaboration with S. Saito (Institute for Molecular Science, Okazaki). Progress on these studies will be described as time permits