Rotationally resolved rydberg absorption of CO2 at 1106 Å. Assignment and analysis of the π 3g3pπu3Σ –uâ†�X1Σ +g Transition

Abstract

The gas-phase absorption spectra of ¹²CO₂ and ¹³CO₂ have been photographed between 880 and 2000 Å at a resolution of 0.008 Å. The diffuse character of most of the bands in this region was confirmed, but the considerable increase in resolution (× 25) over previous work has enabled us to observe some rotationally resolved bands. Our results show that some previous band assignments in the vacuum ultraviolet spectra of CO₂ must be revised. Analysis of the 1106 Å band of both isotopic species provides molecular constants for its upper electronic state, which is shown to be linear. The 1106 Å band is assigned as the origin of the Rydberg forbidden transition ⋯π³_g³3pπ_u³Σ^–_uâ†�X¹Σ⁺_g of CO₂. The v₂ bending vibration of the ³Σ^–_u state is found to have a value of 498 cm^–1 in ¹²CO₂(483 cm^–1 in ¹³CO₂) from assignment of the 2¹₁ transition. Our results are used to interpret some aspects of the excitation spectrum and yield of CO₂ photodissociation.