A study of the vibronic structure in the Hel excited photoelectron spectrum of CO2 involving the X (2)Pi(g) and A (2)Pi(u) Ionic states

The HeI excited photoelectron spectrum of CO2 molecule covering the X (2) Pi(g) and A (2) Pi(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 (2) Pi(g) state, the nu(2) and nu(3) modes are observed to be excited in both an odd and even numbers of quanta in addition to the nu(1) mode, whereas for the A (2) Pi(u) state the spectrum is dominated by excitations of the nu(1) mode alone and in combinations with excitations of the nu(2) mode 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. (C) 1996 American Institute of Physics.