Phonon-Induced Fine Structure of Excitons in Solid Nitrogen

Results of quantitative high-resolution absorption measurements in the range of the $w{}_{}{}^1{}_{}{}^{}\Delta _{\mathrm{u}}^{}{}_{}{}^{}\leftarrow X{{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{g}}^{}{}_{}{}^{}}^{+}$ and $a{}_{}{}^1{}_{}{}^{}\Pi _{\mathrm{g}}^{}{}_{}{}^{}\leftarrow X{{}_{}{}^1{}_{}{}^{}\Sigma _{\mathrm{g}}^{}{}_{}{}^{}}^{+}$ derived exciton progressions in solid ${\mathrm{N}}_2$ are reported. The newly observed detailed fine structure of the vibrational bands is analyzed in terms of a sharp zero-phonon line and phonon-assisted exciton transitions. A theoretical analysis based on a strong-exciton-phonon-coupling model leads to good agreement with the observed experimental line shape.