Raman spectra of CO
2 and the van-der-Waals compound He (N
2)
11 were obtained under nearly hydrostatic pressures up to 40 GPa. The pressure induced changes of the librational spectra suggest that solid CO
2 does not transform directly from phase-I (cubic Pa
3) to phase-III (orthorhombic Cmca). An intermediate phase-IV. which may involve only minor modifications of phase-I, is formed prior to the transition to Cmca structure. P hases IV and III coexist over some pressure range. The pressure shifts of all four Raman active librons of phase-III were determined over a wide pressure range and are compared to previous theoretical results. Spectra of external and internal modes of the van-der-Waals compound He (N
2)
11 are very similar to those of ε-N
2 and imply a close relationship between the structures of He (N
2)
11 and ε-N
2. The observed splitting of the main vibron of isotopic species
14N-
15N indicates that in addition to factor-group interactions site effects are responsible for the observed splittings of the
14N
2 main vibron of He (N
2)
11.
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