Submillimeter-Wave Spectroscopy of HNC Produced in an Extended Negative Glow Discharge

Submillimeter-wave transitions of HNC are observed in an extended negative glow discharge. The measurements of the rotational lines in the ground state, as well as in the vibrational fundamentals, are extended to higher J values (up to J=9←8 in the 830-GHz region). The lines in the higher vibrational excited states ν₂+ν₃, 2ν₂, and 2ν₂+ν₃ are also observed and assigned, using the frequency-magnetic field double modulation technique. Dramatic enhancement of the signal intensity strongly suggests that HNC is predominantly produced in the extended negative glow discharge through the dissociative recombination of HCNH⁺ with electrons.