Knowledge Bank

Electronic transition moment functions have been calculated from SCF, MCSCF, PNO-CI/CEPA, and MCSCF-CI wavefunctions. For CH and OH, the influence of the atomic basis set and of the size of the configuration expansion on the transition moments has been studied, and electron correlation is found to have a large effect on the results. SCF and compact MCSCF wavefunctions are not capable of yielding reliable transition moments, i.e, all the hydride lifetimes calculated from such wavefunctions are too small by 50-100 percent. The lifetimes obtained from MCSCF-CI or PNO-CI/CEPA wavefunctions, however, agree within 10-15 percent of reliable experimental data. For the lowest vibrational levels of the A states of $CH,OH,HF+$, and $HCl+,$ the MCSCF-CI lifetimes are (experimental values in brackets): 531 ns (536), 590ns (690), $26.2\mu s(7.2)$, and $2.51\mu s$ (2.58), respectively. According to these results the experimental value for $HF+$ appears to be considerably too low.