Department of Physics Papers

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Journal Article

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Physical Review B





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We compare the results of the recently published anharmonic theory of librons to the best available data on the libron Raman frequencies. This allows us to deduce a refined estimate of the effective value of the intermolecular quadrupolar coupling constant Γeff for solid H2 and D2. The effect on the librons of virtual transitions to the (J=3) rotational state is included with the result that Γeff is decreased. Our estimate from the optical data is then Γeff=0.72±0.04 and 0.58±0.03 cm−1 for D2(x=1) and H2(x=1), respectively, at zero pressure, where x denotes the mole fraction of J=1 molecules. We also use the anharmonic density of states to analyze specific heat and (∂P/∂T)V data from which we obtain the average libron energy as a function of x. For D2(x=1) the result is Γeff=0.70±0.04 cm−1. Measurements of the conversion-induced pressure change in H2 give Γeff=0.56±0.03 cm−1. Both these determinations are in good agreement with the results from optical data for librons. Furthermore, it is found that there is no significant difference between Γeff(x=1) and Γeff determined from pair spectra in H2 and D2 with x≪1. The anharmonic density of states is also used to interpret the infrared absorption sideband spectrum for the creation of a vibron plus libron(s). The part of the spectrum which we attribute to one-libron processes has a width in agreement with this model and as expected there are two-libron processes resulting from cubic anharmonic libron-libron interactions. Incoherent-neutron-scattering data is also consistent with the anharmonic-libron spectrum.


At the time of publication, author A. Brooks Harris was affiliated with Oxford University. Currently, he is a faculty member in the Department of Physics at the University of Pennsylvania.



Date Posted: 12 August 2015

This document has been peer reviewed.