A multiconfiguration self-consistent-field response study of one- and two-photon dipole transitions between the X 1Σ+ and A 1Π states of CO

Abstract

The one- and two-photon dipole transitions between the X 1Σ+ and the A 1Π states of CO have been studied by means of multiconfiguration self-consistent-field linear and quadratic response methods. The vibrationally averaged oscillator strength for the 0–0 one-photon dipole transition between the X 1Σ+ and A 1Π states obtained using the linear response method is 1.31×10−2 as compared to the experimental results of 0.96(14)×10−2, 1.08(7)×10−2, and 1.11×10−2. The two-photon transition probability rate constant, obtained using the quadratic response method, for the 0–1 vibrational band of the X–A transition of 7×10−59 cm4 s is more than six orders of magnitude smaller than the experimental result of 3.5×10−52 cm4 s. We suggest that the experiment should be reconsidered. The dipole moment of the A 1Π state obtained from quadratic response calculations on the ground state at R=2.332 a.u. is −0.0441 a.u. suggesting an anomalous polarity also for the A 1Π state. The experimental value is ±0.059(20) a.u.