The rotational transitions of hydrogen isocyanide (HNC) and deuterium isocyanide (DNC) in the vibrationally excited states as well as in the ground states were observed in the millimeter and submillimeter wave region. These compounds were generated in a dc glow discharge plasma containing hydrogen (or deuterium), nitrogen, and carbon atoms. The stretching vibrational modes, y1 and y3 states, were selectively excited in the discharge plasma; on the other hand, the bending mode vZ state was

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... lly populated at the cell temperature. The precise rotational, centrifugal distortion and Z-type doubling constants were obtained for all of the first vibrationally excited states as well as the ground states. The experimental equilibrium rotational constants B, are 45 496.7769(45) and 38 207.7217( 105) MHz for HNC and DNC, respectively, where uncertainties correspond to one standard deviation. The equilibrium internuclear distances are also determined to be r, (H-N) =0.996 0643(29) A and r, (NrC) = 1.168 3506( 16) A.