The X̃ 1A1 → Ã 1B1 transition moment of H2O using state-specific configuration-interaction wave functions

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Abstract
We report the results on the oscillator strength of the H2O X̃ 1A1 → Ã 1B1 transition from two types of calculations. One from using correlated state-specific wave functions for each state and one from using large MRD-CI wave functions with a common basis set. In the first case nonorthonormality is considered explicitly via the use of corresponding orbitals. Both types of calculation converge to a value of f=0.065. This result agrees with one experimental value (f=0.060) and disagrees with the most recent theoretical calculation which employed the Stiltjes imaging method (f=0.021). As is the case with previous atomic calculations, the state-specific approach improves the quality of the wave functions of excited states while reducing their size considerably.