Experimental and theoretical studies on Rydberg states of CH2CO in the region 120-220 nm

Absorption spectra of CH2CO and CD2CO in the region 120-220 nm were recorded with a continuously tunable light source of synchrotron radiation. Our spectra show improved sensitivity and resolution with no interference from continuous absorptions reported previously. Transitions to Rydberg states associated with excitation to 3s-9s, 3p(x)-5p(x), and 3d orbitals are assigned based on observed vibronic patterns, isotopic shifts, effective quantum numbers, and comparison with vertical excitation energies predicted with theoretical calculations using time-dependent density functional theory (TD-DFT). Several transitions are reassigned and new vibrational progressions are identified for some Rydberg states. The major active modes for the ns Rydberg series are the Cdouble bondC stretching (nu(4)) and the Cdouble bondO stretching (nu(2)) modes; the CH2 scissor (nu(3)) mode is also active in several transitions. TD-DFT using a polarized basis set (PBS) proves to be an excellent method for predictions of vertical excitation energies and oscillator strengths, especially for higher Rydberg states. (C) 2002 American Institute of Physics.