A study of the vibronic structure in the Hel excited photoelectron spectrum of CO₂involving the X ²Π[sub g] and A ² Π[sub u] ionic states

Abstract

The HeI excited photoelectron spectrum of the CO₂molecule covering the X ²Π[sub g] and A ²Π[sub u] ionic states has been recorded at a resolution of better than 5 meV. Complex vibrational structures are resolved in both photoelectron bands. In the X ²Π[sub g] state, the v₂and v₃modes are observed to be excited in both an odd and even numbers of quanta in addition to the v₁mode, whereas for the A ²Π[sub u] state the spectrum is dominated by excitations of the v₁mode alone and in combinations with excitations of the v₂mode in two quanta involving strong Fermi resonance. The observed spectrum has been assigned by comparison with optical spectra and with calculations of the vibrational fine structure including vibronic and spin–orbit coupling.