COMPUTATION OF ELECTRONIC-TRANSITION MOMENTS - THE LENGTH VERSUS THE VELOCITY REPRESENTATION

We have compared transition moments (TMs) obtained using the length and velocity representations for transitions from the ground state of H-2 to the lowest two 1-PI-u and two 1-SIGMA-u+ Rydberg states, the A1-PI-X1-SIGMA+ transition in BH, and the A1-PI-u-X1-SIGMA-g+ transition in C2. For H-2, the TMs in the length and velocity representations agree well even in cases where the one-particle basis is incomplete and the TM has not converged. For BH and C2 the TM in the length representation converges rapidly with improvements in the one-particle basis set and is insensitive to inner-shell correlation. In contrast, in the velocity representation convergence with improvements in the one-particle basis is much slower, especially for C2, and the TMs are significantly changed by inner-shell correlation. Thus the difference between the TMs in the length and velocity representations would not appear to be a viable diagnostic of TM convergence.