High resolution infrared spectroscopy of the ν1 (NH stretch) and ν2 (CH stretch) bands of HCNH+

The infrared spectrum of the ν1-band (NH stretch) and the ν2-band (CH stretch) of protonated hydrogen cyanide HCNH+ has been observed based on recent theoretical predictions. This is the first observed spectrum of this ion in any wavelength region. From a least-squares analysis of the rovibrational bands, the following spectroscopic constants have been obtained (in cm−1): ν1 (NH stretch) ν2 (CH stretch) ν0 3482.844 1(10) 3187.863 8(4) B1 1.228 633(39) 1.228 494(19) B0 1.236 024(37) 1.236 067(18) D1 1.574(43)×10−6 1.610(22)×10−6 D0 1.596(42)×10−6 1.620(21)×10−6 It is hoped that the rotational constants determined in this paper will lead to the identification of the microwave spectrum of this molecule in interstellar space.