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 resoluti on of better than 5 meV. Complex vibrational structures are resolved i n 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 o f quanta in addition to the nu(1) mode, whereas for the A (2) Pi(u) st ate the spectrum is dominated by excitations of the nu(1) mode alone a nd in combinations with excitations of the nu(2) mode in two quanta in volving strong Fermi resonance. The observed spectrum has been assigne d by comparison with optical spectra and with calculations of the vibr ational fine structure including vibronic and spin-orbit coupling. (C) 1996 American Institute of Physics.