HIGH RESOLUTION SPECTROSCOPY AND ANALYSIS OF THE $v_{4}$ BAND OF METHYL ISOCYANIDE

Abstract

The first completely-resolved vibration-rotation spectroscopy of methyl isocyanide ($CH_{3}NC$) has been performed using a high resolution Fourier Transform Spectrometer. The $v_{4}$ fundamental band has been measured in the region between 900 to $990 cm^{-1}$ region with a Doppler-limited resolution of $0.004 cm^{-1}$. 971 transitions have been assigned to the P and R branches of the $v_{4}$ fundamental band spanning from $K = 0$ to $K = 9$ and $J = 0$ up to $J = 65$. Reliable and high accuracy sets of molecular constants for both the $v_{4}$ and ground states have been obtained. Small anomalies found in a small group of lines (16) in the low-J region of $K = 4$ subband and around $J = 61$ of the $K = 3$ subband. Perturbation analysis has been performed based on the Amat rule and symmetry discussion. A rotational resonance ($\Delta l = \pm1, \Delta k = \pm 2)$ between the $v_{4}$ and $3v_{8}^{\pm 1}$ has been traced to be the origin, of the anomalies and the interaction matrix element has been derived. The results of the assignment and analysis of the $v_{4}$ band of methyl isocyanide will be presented, and the molecular constants for both the ground slate and the $v_{4}$ fundamental will be reported.""