Ab initio spin-orbit CI calculations of the potential curves and radiative lifetimes of low-lying states of lead monofluoride

Abstract

The electronic structure of the lead monofluoride molecule is studied by means of ab initio configuration interaction ͑CI͒ calculations including the spin-orbit interaction. Potential-energy curves are generated for a large number of electronic states, of which only the X 1 2 ⌸ 1/2 ground and X 2 2 ⌸ 3/2 and A 2 ⌺ ϩ excited states have been observed experimentally. Two different methods are compared for the inclusion of spin-orbit effects in the theoretical treatment, a contracted CI which employs a basis of large-scale ⌳ -S eigenfunctions to form a rather small matrix representation of the full relativistic Hamiltonian ͑two-step approach͒, and a more computationally laborious technique which involves solution of a secular equation of order 250 000 S 2 eigenfunctions of different spin and spatial symmetry to achieve a potentially more evenly balanced description of both relativistic and electron correlation effects ͑one-step approach͒. In the present application, it is found that both methods achieve quite good agreement with measured spectroscopic constants for the X 1 , X 2 , and A states. The simpler of these methods is also employed to predict the radiative lifetimes of the latter two states. The key A 2 ⌺ ϩ -X 2 ⌸ transition moment in these calculations is found to vary strongly with internuclear distance and to vanish in the neighborhood of the respective equilibrium distances of both participating states. The computed lifetime for the A, vЈϭ0 state of 16 s overestimates the corresponding measured value by a factor of three, but those of higher vibrational states are found to decrease rather sharply with increasing vЈ, suggesting that only a slight displacement of the theoretical A -X transition moment curve is needed to explain the above discrepancy.

Precision measurements with polar molecules: the role of the black body radiation

“…Their study is therefore challenging for both theoretical and experimental investigations. Among the molecules mentioned above, YbF [22,23] and PbF [24] have been studied from ab initio theory and dipole moment function of YbF and its value and first derivative for PbF at the equilibrium internuclear distance have been derived.…”

Spectroscopic constants of the known electronic states of lead monofluoride

“…Determination of T 0 of the B state requires both our observations and the spin rotational constants of Ziebarth [7] and Lumley and Barrow [4]. Table 2 presents a summary of experimentally determined values of T 0 along with the ab initio calculations of Das [9]. All but the E and F states can easily be identified with the calculation.…”

Modelling X-ray scattering factors from fluids of some fluorinated molecules and related compounds

“…Two further molecules, PbF and GdF, are of interest with the present focus on fluorinated molecules. The recent study by configuration interaction [22] shows that at the experimental equilibrium separation of PbF, it has the ionic form Pb þ F À . Thus, this can be modelled usefully once a relativistic scattering factor f(k) for Pb þ becomes available, the f(k) for F À being already given by Rez et al [16].…”