Calculation of dynamically induced electronic transitions of matrix-isolated atomic nitrogen

The parity-forbidden transitions 2P→2D and 2D→4S within the ground configuration (2p)3 of atomic nitrogen have been observed as phonon- and vibron-induced emission bands in luminescence spectra of solid nitrogen and have been attributed to dipole radiation induced by dynamic crystal fields of odd parity with respect to the substitutionally trapped atom in the N2 lattice. We confirm this interpretation by an a priori calculation of the absolute transition probabilities and band shapes, using known atomic, molecular, and crystal properties of nitrogen and no adjustable parameters. The induced dipole moments are calculated from the vibrationally modulated quadrupole fields of the host molecules at the site of the polarizable guest atom. The dynamics of the doped lattice are treated by a normal-coordinate analysis of the ’’supermolecule’’ consisting of the atom and its 18 nearest radially relaxed N2 neighbors suspended in the unperturbed surrounding N2 lattice. The calculated dipole-weighted densities of phonon states and the resulting total transition probabilities agree well with observations. The corresponding emissions in rare-gas matrices are represented via superpositions of empirical pair overlap dipole moments.