Infrared Spectrum of Isoselenocyanic Acid, HNCSe

The preparation of gaseous isoselenocyanic acid, HNCSe, first reported by Landsberg [10] in 1979, has been considerably improved. This unstable molecule decays in the gaseous phase according to a second‐order reaction. In the infrared region the vibrational spectrum of HNCSe was measured in the gaseous phase and in an argon matrix at low resolution. The combined analysis of the vibrational spectra of HNCSe yielded the assignment of the A fundamental vibrations. From the gaseous phase absorptions v 4 = 3535 cm −1 , v 2 = 1957 cm −1 and v 3 = 625 cm −1 could be assigned. The bands in the gas phase spectrum at 760, 583, 521 and 419 cm −1 cannot be considered as band centers. They are the result of the superposition of the subband structures of the bending modes v 4 , v 5 and v 6 exhibiting quasilinear behaviour. This can be deduced from the wavenumber positions of v 4 = 508 cm −1 and v 5 = 419 cm −1 observed in the argon matrix spectra. Due to the rapid H/D exchange the infrared spectrum of DNCSe could not be measured.