THEORETICAL PREDICTION OF THE ELECTRONIC EXCITED-STATES AND RESONANCERAMAN INTENSITIES IN FORMAMIDE FROM COUPLED-CLUSTER CALCULATIONS

Electronic excitations and the resonance Raman spectrum of formamide w ere obtained from ab initio electron correlation calculations using th e equation of motion coupled cluster (EOM-CCSD) method. Interpretation of the UV spectrum on the basis of calculated vertical excitation ene rgies and oscillator strengths accounts for all experimental bands pre viously assigned. Our assignment, however, suggests an additional Rydb erg band at about 7.4 eV which may be hidden under the main absorption . We also show that the Rydberg states appear pairwise, corresponding to n and pi hole states, respectively. Using analytic derivative techn iques, derivatives of the excited state energies with respect to norma l coordinates of the ground state were calculated. Approximate resonan ce Raman intensities have been determined. (C) 1997 Published by Elsev ier Science B.V.