Induced intensity and band shape of the <i>w</i> 1Δ<i>u</i>←<i>X</i> 1Σ+<i>g</i> system in pure solid α-N2

The crystal-field induced intensity and the band shape of the w 1Δu←X 1Σ+g transition in pure solid N2 are treated theoretically. The static crystal field generated by the molecular quadrupoles mixes 1Δu and 1Πu states and its magnitude suffices to explain the observed intensity of the transition in the solid. The band shapes can be interpreted as Stokes-type multiphonon structures due to totally symmetric local breathing modes with a weaker librational contribution. The dependence of the Stokes parameter and of the widths of the zero- and one-phonon bands on the intramolecular Franck–Condon factor illustrates that the Stokes-type excitation of phonons is diminished by increased delocalization through intermolecular vibronic resonance.

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