Laser induced bound–bound and bound–continuum emission of the Sr2 A 1Σ+u–X 1Σ+g system

Laser-induced emission of the Sr2 molecule consisting of discrete molecular fluorescence series, regularly modulated continuous fluorescence and an unstructured continuum was observed in the gas phase at excitation wavelengths between 600 and 450 nm. The analysis of the molecular line spectra provides Dunham coefficients and RKR potentials for the X 1Σ+g ground state and the excited A 1Σ+u state. The main spectroscopic constants are ωe=40.32 cm−1, Re=4.45 Å and De=1060 cm−1 for the X state and ωe=85.07 cm−1, Re=3.95 Å and De=5400 cm−1 for the A state. The modulated continuum which is due to bound-continuum transitions from a specific exited level v′, j′ to the continuum of the ground state was used to determine the repulsive part of the ground state potential up to 3000 cm−1 above the dissociation limit. Calculated discrete and continuous Franck–Condon factors are in good agreement with the experiment, both depend sensitively on the rotational quantum number J. The unstructured continuum can be interpreted as a quasicontinuous superposition of many fluorescence spectra. Calculations show that laser excitations from levels v″, J″ slightly below the dissociation limit and excitation from continuous states lead to the observed continuum.