On the Near Infrared Absorption Spectrum of Mono-Deutero-Acetylene

The absorption spectrum of mono-deutero-acetylene has been photographed over the region 6000-10,500A in the first order of a 21-foot grating using absorbing columns up to 20 feet in length at atmospheric pressure. One band was found with origin at 10,302A. It is attributed to the molecule ${\mathrm{C}}_2$HD. From the rotational constants of the band and similar data from the ${\mathrm{C}}_2$ ${\mathrm{H}}_2$ bands, the interatomic distances in acetylene are computed as $r_{\mathrm{CC}}=(1.247\mathrm{}\pm 0.008)\times {10}^{-8\mathrm{}}$ cm and $r_{\mathrm{CH}}=r_{\mathrm{CD}}=(0.940\mathrm{}\pm 0.036)\times {10}^{-8\mathrm{}}$ cm.