Rotationally resolved rydberg absorption of CO₂at 1106 Å. Assignment and analysis of the π3g3pπ_u³Σ–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 ⋯π3g33pπu3Σ–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.