Precise Rotational and Hyperfine Parameters of Nitrosyl Chloride Obtained Using a Cavity Pulsed Microwave Fourier Transform (MWFT) Spectrometer

Author Institution: Department of Chemistry, University of British Columbia; Walther-Nernst-Institut, Humbolt-Universit\""{a}t; Department of Chemistry, University of British ColumbiaThe pure rotational spectra of 5 isotopic species of nitrosyl chloride, $^{35}Cl^{14}N^{16}O, ^{37}Cl^{14}N^{18}O, ^{35}Cl^{13}N^{16}O, ^{37}Cl^{15}N^{16}O$ and $^{35}Cl^{14}N^{18}O$ have been measured using a cavity pulsed microwave Fourier Transform spectrometer. The high sensitivity of this spectrometer allowed us to measure {a}-type spectra of all 5 isotopomers in natural abundance. We have also observed weak {b}-type spectra of the first four isotopomers, the latter three of these for the first time. An enriched sample was used to measure {b}-type transitions for the $^{15}N$ isotopomers. Precise values for the rotational constants and the quartic centrifugal distortion constants have been obtained, and the centrifugal distortion constants have been used in a refinement of the harmonic force field. The hyperfine structures show small effects (up to $\sim$50 kHz) arising from spin-rotaion coupling and some what larger effects (up to $\sim$1.5 MHz) arising from accidental near--degeneracies of the rotational energy levels. These deviations have allowed us to calculated spin-rotaion constants and off-diagonal quadrupole coupling constants, $\chi_{ab}$, for both Cland N. The quadrupole coupling tensors have been diagonalized