High-resolution spectroscopy and the analysis of ro-vibrational transitions of molecules in solid parahydrogen

Solid parahydrogen provides a novel matrix for isolation spectroscopy of atoms and molecules. Ro-vibrational motion of molecules embedded in solid parahydrogen is well quantized on account of the weak interactions in the crystal and of the softness of the crystal being characteristic of quantum crystals. Most of the observed spectral linewidths are one or two orders of magnitude sharper than those observed in conventional rare gas matrices. The sharp linewidths make the parahydrogen crystal an excellent matrix for the study of ro-vibrational states and dynamics of dopant molecules in the condensed phase by high-resolution spectroscopy. In this article, we have summarized the most fundamental part of our study, that is, the theory of ro-vibrational states of dopant molecules in the crystal, which is necessary for the quantitative analysis of high-resolution infrared spectra. We also discuss what we have learned from the analysis of high-resolution infrared spectra in solid parahydrogen. These include perturbations to rotational motion of dopant molecules, reduction of rotational constants, vibrational dephasing and relaxation. Outstanding questions to be solved are also discussed herein. # 2003 Elsevier B.V. All rights reserved.