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Low-frequency Raman spectra ͑up to 800 cm Ϫ1 ) measured below 18 K are reported for the entire pressure range of phase I of para-hydrogen doped with low fractions of the ortho-modification. In addition to bands corresponding to the E 2g optical phonon and the Jϭ2←0 rotational transitions, we observed a weak band attributed as S 0 (1). These spectra are employed to deduce information on the interactions that play a decisive role in bringing about the transition to the broken symmetry phase II. A new theoretical analysis is presented to understand the rotational Raman excitations and the role of various pairwise anisotropic interactions between H 2 molecules. In order to explain the pressure dependence of the S 0 (0) and S 0 (1) bands, we infer that a fourth-harmonic crystal field is present. The frequencies of the S 0 (0) and S 0 (1) bands are used to reconstruct the respective crystal field parameter.

Details of the crystal structure and quantum chemistry calculations of the title mol­ecule, C13H9BrO, illustrate the effects of intermolecular interactions and the substitution of one of the two aromatic rings on the molecular conformation. The asymmetry of the mol­ecule is documented by the two Caryl—Caryl—C=O torsion angles of −68.3 (5) and −17.6 (6)°. A C—H·O hydrogen bond [H·O = 2.5 Å, C·O = 3.412 (5) Å and C—H·O = 174°] and a C—H·π contact involving the H atom at position 4 of the substituted ring and the π‐system of the unsubstituted ring of an adjacent mol­ecule [H·Cg = 2.96 Å, C·Cg = 3.806 (5) Å and C—H·Cg = 153°; where Cg is the centroid of the unsubstituted ring] are observed in the crystal structure.

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