Electronic transition dipole moment function of the f' 0+ (1D2) – X1Σ+ transition of ICl

Abstract

The transition dipole moment (TDM) function of the f′ 0+ (1D2) – X1Σ+ transition of ICl is determined in the range 2.76 – 3.49 Å from analyses of fluorescence spectra and data on the f′ 0+ (1D2) state lifetime. The TDM function in the specified range shows non-monotonic dependence with a maximum at R ≈ 2.9 Å. Ab initio calculations carried out using the complete active space self-consistent field method followed by calculations that take into account the dynamic electron correlations and spin–orbit interaction reproduce reasonably well the shape of the experimental TDM function. It is shown that the f′ 0+ (1D2) state near its equilibrium internuclear distance (Re = 3.226 Å) consists mainly of the ls-state 3 1Σ+ which is optically coupled with the ls-state 1 1Σ+, the dominant component of the X1Σ+ state in this R-region. The non-monotonic behavior of the f′ 0+ (1D2) – X1Σ+ TDM function at shorter distances is mainly due to spin-orbit interaction between the ls-states 3 1Σ+ and 3 3Π. The potentials of these ls-states cross at R ≈ 2.6 Å that leads to decrease in the weight of 3 1Σ+in f′ 0+ (1D2) and, as a consequence, to a non-monotonic TDM function of the f′ 0+ (1D2) – X1Σ+ transition. The TDM functions of the transitions from f′ 0+ (1D2) to other 0+ valence states were also calculated. The behavior of these TDM functions is qualitatively interpreted in terms of the R-dependence of the weights of the optically coupled ls-states.