Intensities of multipole-induced zero-phonon transitions in solid parahydrogen

Theoretical expressions are given for the intensities of zero-phonon single and double transitions in solid parahydrogen arising from the isotropic 2ˡ multipole induction mechanism. Comparisons between theory and experiment for l=2 and 4 [corresponding to Sv'(0) and Sv'(0)+Qv''(0) and Uv'(0) and Uv'(0)+Qv''(0) transitions, respectively] have been given previously, and the results are in reasonably good agreement. A direct comparison is not possible for the recently observed l=6 [Wv'(0) and Wv'(0)+Qv''(0)] transitions because of the unavailability of ab initio values of the vibration-rotational matrix elements of the 64-pole moment function, or for the as yet unobserved l=8[Yv'(0) and Yv'(0)+Qv''(0)] transitions. Modifications of the intensities of the Wv'(0) transitions due to the mixing of rotational levels by the quadrupole-quadrupole interaction have been calculated, and they contribute less than 1%. These corrections are smaller than those due to phonon renormalization and thus will not appreciably affect the magnitudes of the 64-pole moment matrix elements deduced from the experimental intensities.