Spectroscopy of pendular states: Determination of the electric dipole moment of ICl in the X 1Σ+(v″=0) and A 3Π1(v′=6–29) levels

In this paper, we describe new measurements of the electric dipole moment of ICl A and X states. These measurements are deduced from a Doppler free laser induced fluorescence spectroscopy of the A-X transition and concern the X v′′=0 and 17 vibrational levels of the A state. A complete modelization of the spectra has been developed and the accuracy of these measurements is rather high. We have been able to invert in an approximate manner the vibrational dependence of the A state dipole moment to get its dependence with the internuclear distance r. The observed dependence at large r is well rationalized by the model of an ionic–covalent avoided crossing, and appears to be very close to the result of an ab initio calculation of the same state of IF molecule.