ROTATION VIBRATION SPECTRUM OF HCN

Abstract

More than 40 bands of the HCN molecule are available for performing the vibrational analysis. About 20 of these bands in the $1.1 \mu$ to $3.0 \mu$ region some of which have been observed for the first time, have been measured or remeasured. Q branches for most of the perpendicular bands have been resolved, allowing a precise determination of the band origins. It has been necessary to make use of the ten $Y_{ilk}$ coefficients to perform a satisfactory vibrational analysis. A number of cases of Fermi resonance have been observed. Several of these perturbations can be calculated from the observed anomalous B values. The B values have shown that it is necessary to introduce the six $\gamma$ terms into the expression for $B_{e}$. More than a dozen $HC^{13}$N bands have been observed and measured. It has been possible to obtain a very precise frequency for the fundamental band $(01^{1}-000)$ by application of the Ritz Combination principle to the near infrared harmonic bands. Five independent determinations of this band frequency have been obtained for $HC^{12}N$ and three for $HC^{13}N$.