Knowledge Bank

The $S3(0)$ transition $(\nu =3\leftarrow 0,J=2\leftarrow 0)$ in solid para-hydrogen has been observed at $12058.982cm-1$ with a width of $0.252cm-1$ (FWHW). The line width of his transition is broader than that of the pure rotational $S0(0)$ transition. Although linewidths usually narrow with vibrational excitation due to a larger phonon-excitation energy discrepancy and diminished coupling among molecules, all observed $S\nu (0)(\nu =\nu \leftarrow 0,J=2\leftarrow 0$, for $\nu ;=1,2,3$) transitions exhibit linewidths which are larger that that of the pure rotational transition. The $S\nu (0)$ linewidths are shown to be a result of the mixing of the simultaneous state $Q\nu (0)+S0(0)$ manifold $(\nu =\nu \leftarrow 0,J=0\leftarrow 0$, and $\nu =\nu \leftarrow 0,J=2\leftarrow 0,$ respectively, for two neighboring molecules) into the Zeroth order $Sv(0)$ manifold. The linewidths of all $Sv(0)$ transitions were reproduced theoretically by considering the consequences of simultaneously placing two excitons, $Qv(0)$ and $SO(0)$ in the lattice. By considering the roton’s dephasing due to the presence of the simultaneously-created $Qv(0)$ excitation, one can calculate the contribution of this coherence relaxation (i.e. $T2$ relaxation) process to the overall frequency uncertainty of each $Sv(0)$ transition.