Fourier transform millimeter-wave spectroscopy of chlorocarbene (HCCl)

The 1(01)-0(00) and 2(02)-1(01) rotational transitions of (HCCl)-Cl-35 and (HCCl)-Cl-37 in the (H) over tilde (1)A(') ground vibronic state have been observed with a Fourier transform millimeter-wave spectrometer. The HCCl molecule is produced by discharging a gaseous sample of CH2Cl2 diluted in Ar with a pulsed discharge nozzle. The effective rotational constant (B+C)/2, the centrifugal distortion constant Delta (J), the nuclear quadrupole interaction constants, and the nuclear-spin rotation interaction constant are determined for each isotopic species. The nuclear-spin rotation interaction is found to make a significant contribution to the hyperfine structure of this molecule, which originates from the relatively low-lying electronic excited state. The nuclear quadrupole interaction tensor is highly asymmetric, indicating a significant pi character of the C-Cl bond. This can be interpreted in terms of the backdonation of pi electrons from the chlorine atom to the carbon atom. (C) 2001 American Institute of Physics.