INFRARED MATRIX-ISOLATION STUDIES OF METHANE NITRIC-ACID SYSTEM

The infrared spectra of CH4/HNO3/Ar matrices and their deuteurium analogs have been studied in the concentration range (1/1/1000)-(16/2/1000). The spectra prove the formation of a well-determined 1:1 CH4 ... HNO3 complex and suggest an existence of(CH4)(n)HNO3 aggregates of relatively well-defined geometry. The perturbed nitric acid fundamentals were identified for all 1:1 complexes between CH4, CD4 and HNO3 DNO3. The relatively strong perturbation of OH (OD) group vibrations indicates the complex geometry with the OH group directed towards a face of the methane tetrahedron and formation of the weak hydrogen bonding between nitric acid and methane molecules. The temperature reversible fine structure of the two absorptions due to the OH stretching and NOH in plane bending vibrations in the spectra of CD4 ... HNO3 complexes suggests that methane molecule undergoes hindered rotational motion in the complex. The formation of the CH4 ... HNO3 complex does not affect, or affects insignificantly, the photolytical behavior of HNO3 in solid argon.