Knowledge Bank

The infrared absorption spectrum of $C2H2$ has been studied in the region from 2500 to $4150cm-1$. Nineteen bands were observed of which eleven were sufficiently intense and well resolved to permit rotational analysis. Five bands involving the ground vibrational state were analysed giving the rotational constants $B0=1.17654\pm 0.00004$ and $D0=1.51\pm 0.03\times 10-6$ $cm-1$. The \emph{l}-doubling constants for the degenerate modes were determined to be $q4=5.27,q5=4.63\times 10-3$ $cm-1$. The rotational constants determined for the various observed states clearly show that additional data will be needed and due account taken of resonances to obtain a satisfactory set of rotational constants. The use of difference bands involving the $v1=1$ level permits the determination of the vibrational frequency of that level to be $612.88cm-1$.