The infrared spectrum of fulminic acid,HCNO, in the ν4 fundamental region

The infrared spectrum of fulminic acid, HCNO, was measured with high resolution in the region 500–657 cm^?1. The spectrum was obtained with a Bomem interferometer, at a reslution of about 0.006 cm^?1. Thirteen bands could be identified and assigned to rovibrational transitions of HCNO. These are the fundamental ν₄ and some of its hot bands, and the overtone 2ν₅ and some of its hot bands. Because ν₅ is a quasilinear bending mode, the identification and measurement of the various hot bands is especially important for locating the combination states of ν₄ with various quanta of ν₅.