CARS study of deuterium clusters stabilized in solid helium

Solid deuterium clusters that for the first time have been isolated in a matrix of solid helium have been investigated at T=1.3 K and P=3 MPa by the coherent anti-Stokes Raman spectroscopy (CARS) technique. The vibronic Q₁((J=0) and Q₁(J=1) line intensity, shape, and positions have been studied as functions of ortho and para content in the solid, as well as of the size of clusters. The strong effect of Raman scattering cross-section sensitivity to the molecular environment nuclear spin state has been found in CARS: the ratio of probabilities for the scattering by para(J=1) and ortho(J=0) deuterium, which is equal to 1 in a gas, is as high as 10000 in nearly pure ortho deuterium, whereas it is about 50 in spontaneous Raman scattering. This effect has been shown to occur starting from a cluster size corresponding to the onset of the phonon band.