Knowledge Bank

It has been shown that high-resolution infrared spectroscopy is applicable to the zero-phonon transitions of rotons and vibrons in solid hydrogen. Because the pure vibrational transitions $Qn(0)[v=n\leftarrow 0,J=0\leftarrow 0]$ of solid parahydrogen become infrared-active only upon interaction with residual $J=1$ orthohydrogen, studies of the pure vibrational transitions under high-resolution provide detailed and accurate information on intermolecular interactions between hydrogen molecules. Here, we report the high-resolution absorption spectrum of the first overtone pure vibrational transition $Q2(0)$ of solid parahydrogen. The high-resolution spectrum of the $Q2(0)$ transition at around $8070cm-1$ was observed using a difference frequency laser $systema$. The spectrum shows a complicated spectral feature compared with that of the $Q3(0)$ $transitionb$. The $v=3$ vibrational exciton was found to be well localized on the parahydrogen molecule next to an orthohydrogen. On the other hand, since the vibron hopping matrix element of the $v=2$ state is comparable to the energy shift due to the existence of orthohydrogen, the observed rich spectral structure can be interpreted as due to the $v=2$ vibron hopping over a limited number of lattice sites in the crystal. We will discuss the quantitative analysis of the observed spectrum.