Microwave Spectrum of BrCN at Six Millimeters

Abstract

69 lines of the $J=5\mathrm{}\to 6$ 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 ${\mathrm{Br}}^{81}$ ${\mathrm{C}}^{12}$ ${\mathrm{N}}^{14}$.