The absorption spectra of solid CO and N2

Abstract

The absorption spectra of CO and N₂ solids were investigated in the wavelength region 1600–1150 å at temperatures ranging from 10°k to 30°k. For CO two electronic transitions were observed: A ¹II ← X ¹ Σ⁺, 13 vibrational bands measured between 1570 å and 1250 å; d ³ Δ ← X ¹ Σ⁺, 7 vibrational bands measured between 1300 å and 1225 å. The spectra are simply related to the moleculartransitions and can be interpreted on the basis of existing theory of the excited states of molecular crystals of cubic symmetry. Davydov splitting has been clearly resolved for a number of bands of the A ← X transition, and the experimental splitting energy can be quantitatively accounted for if the f-number of this transition is 0·16. The observed relative intensities of the components are in agreement with theoretical prediction. For N₂ also two electronic transitions have been observed: a ¹ II _g ← X ¹ Σ _g ⁺, 8 vibrational bands measured between 1460 å and 1250 å; ω ¹ Δ_μ ← X ¹ Σ _g ⁺, 11 bands measured between 1400 å and 1170 å. Here again Davydov splitting was observed but the theoretical interpretation of the splitting energy and the relative intensities of the components is complicated by the fact that the corresponding molecular transitions are dipole forbidden. The assignment of the lattentransition is confirmed.