Effect of orthohydrogen impurity on the absorption intensities of single transitions in a solid parahydrogen crystal

• Published in: Journal of molecular spectroscopy 2006-02, Vol.235 (2), p.206-210
• Main Authors: Mishra, Adya P., D’Souza, Richard, Balasubramanian, T.K.
• Format: Article
• Language: English
• Subjects: Multipole moments; Phonon renormalization factors; Quantum solids; Zero-phonon single and double transitions
• ISSN: 0022-2852; 1096-083X
• DOI: 10.1016/j.jms.2005.11.006

This paper provides insights for the accurate calculation of theoretical intensities of single transitions in a parahydrogen crystal containing trace amounts of orthohydrogen impurity. From the ratio of the experimental intensity to that of theoretical one ( α ˜ exp / α ˜ th ) we can deduce the value of the phonon renormalization factors, which are not easily amenable for calculations, a priori and are customarily set equal to unity. The ratio α ˜ exp / α ˜ th for S transitions varies over a wide range from 0.15 to 0.94. Different reasons are advanced for this wide variation and remedy suggested. A more careful experimental measurement of the intensity of single transitions in a parahydrogen crystal at different, carefully controlled, orthohydrogen concentrations is desirable. The accurate knowledge of the ratio α ˜ exp / α ˜ th will then lead to a detailed understanding of the theory of phonon renormalization factors in quantum solids.