LABORATORY DETECTION OF $C_{5}$ BY DIODE LASER SPECTROSCOPY.

Author Institution: Herzberg Institute of Astrophysics, National Research Council of CanadaA carbon chain molecule $C_{5}$ has been detected by observing the vibration-rotation bands around the $4.6-\mu m$ region. $C_{5}$ is generated in a hollow cathode discharge in either $C_{2}H_{2}$ or $C_{2}H_{4}$ with He as a buffer gas. The discharge is cooled to $-60^\circ C$ by circulating cooled methanol through copper tubing wound around the cathode, and is amplitude modulated at about 1 kHz. In addition to the fundamental band, hot bands are also observed. The fundamental band is analyzed by using a standard linear molecule vibration-rotation energy expression, and molecular constants thus obtained agree very well with those derived from the analysis of the spectrum observed in the circumstellar shell of$IRC+10216$ by $Bernath^{1}$ et al. Our observation extends to higher-J transitions because of our warmer source, and leads to a better determination of the constants. Analyses of the hot bands are in progress. $^{1}$P.F. Bernath, private communication