Microwave Spectrum of BrCN at Six Millimeters

Abstract

69 lines of the $J=5\ensuremath{\rightarrow}6$ pure rotational spectrum have been measured. Lines were found due to the following molecules in their normal isotopic abundances; ${\mathrm{Br}}^{79}$${\mathrm{C}}^{12}$${\mathrm{N}}^{14}$, ${\mathrm{Br}}^{81}$${\mathrm{C}}^{12}$${\mathrm{N}}^{14}$, ${\mathrm{Br}}^{79}$${\mathrm{C}}^{13}$${\mathrm{N}}^{14}$, ${\mathrm{Br}}^{81}$${\mathrm{C}}^{13}$${\mathrm{N}}^{14}$, ${\mathrm{Br}}^{79}$${\mathrm{C}}^{12}$${\mathrm{N}}^{15}$, and ${\mathrm{Br}}^{81}$${\mathrm{C}}^{12}$${\mathrm{N}}^{15}$. Transitions have been found in the vibrational states (0 0 0), (0 ${1}^{1}$ 0), (1 0 0), (0 ${2}^{0}$ 0), (0 ${2}^{2}$ 0), and (1 ${1}^{1}$ 0). The apparatus is described and experimental results are compared with those of previous investigators. Fermi resonance effects have been observed and analyzed. A dependence of the $l$- type doubling constant on the bromine quadrupole field has been found. Quadrupole coupling constants have been determined for the first excited vibrational states in ${\mathrm{Br}}^{79}$${\mathrm{C}}^{12}$${\mathrm{N}}^{14}$ and ${\mathrm{Br}}^{81}$${\mathrm{C}}^{12}$${\mathrm{N}}^{14}$.