Optical Excitation of the Rotational Transition of Methane in Condensed Rare Gas Matrices

Abstract

The far-infrared optical absorption spectra of CH₄ and CD₄ molecules diluted in condensed Xe, Kr and Ar have been obtained at 6 K. The isotope shifts of the peak energy showed that observed absorption bands are due to rotational transitions and vibrational ones of the substituted molecules. In the Xe matrix the vibrational absorption band has not been found. The observed peak positions of the rotational transitions are compared with a theoretical calculation by Nishiyama and Yamamoto. The agreement between the experiment and the theory is good in the case of the Xe matrix but poor in the Kr and Ar matrices. The discrepancy is discussed in relation to the intensity of the vibrational band.