New Infrared Transitions in Solid Parahydrogen in the MIR and NIR/VIS Regions

✍ Scribed by M. Mengel; B.P. Winnewisser; M. Winnewisser

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 525 KB
• Volume: 188
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1997.7520

✦ Synopsis

We have studied the infrared spectrum of solid parahydrogen at different orthohydrogen impurity levels in the midinfrared (MIR) region between 600-2000 cm 01 and in the near infrared/visible (NIR/VIS) region between 10 000-16 500 cm 01 . The most important new observations in the MIR region, obtained with a single pass through an absorption cell 4.75 cm in length, are the U 0 (0) / S 0 (0) double transition around 1520 cm 01 , broadened to about 20 cm 01 by roton delocalization, and the single orthohydrogen transition U 0 (1) at 1619.12 cm 01 , which was previously observed only in normal hydrogen. For the NIR/VIS measurements an internal multireflection cell with 14-cm absorption path length was used. Of particular interest here is the second overtone band of solid hydrogen including double transitions of the type Q 2 (J) / Q 1 (J) (J Å 0, 1; J Å 0, 1). At 10 241.07 cm 01 the new single transition W 2 (0) could be observed. For several double transitions in the NIR/VIS region a fine structure is observed, which can be explained by anisotropic interaction in rotationally excited pairs of molecules. The treatment of the fine structure of the Q 2 (0) / S 1 (0) transition leads to the prediction of a considerable intensity of the triple transition Q 2 (0) / Q 1 (0) / S 0 (0). Stimulated by this result we have found the triple transitions Q 1 (0) / Q 1 (0) / S 0 (0) at 8660 cm 01 and S 1 (0) / Q 1 (0) / S 0 (0) at 8990 cm 01 in the first overtone region. At 12 788 cm 01 we detected an absorption feature that we have assigned to the triple transition S 1 (0) / Q 1 (0) / Q 1 (0). We explain the infrared activity of this transition in terms of a three-body process, a dipole moment induced within a triplet of hydrogen molecules by successive pairwise induction.