Vibrational energies and full analytic potential energy functions of PbI and InI from pure microwave data

Pure rotational spectra of PbI and InI are interpreted to yield a full analytic potential energy function for each molecule. Rotational spectra for PbI have been retrieved from literature sources to perform the analysis. Rotational transition frequencies for excited vibrational states of InI (0. <. . v . <. 11) are measured during this work. Ignoring hyperfine splittings, . Bv and . Dv values are used to generate a set of "synthetic" pure . R(0) transitions for each vibrational level. These are then fitted to an "Expanded Morse Oscillator" (EMO) potential using the direct-potential-fit program, . dPOTFIT. The well-depth parameter, . De, is fixed at a literature value, while values of the equilibrium distance . re and EMO exponent-coefficient expansion (potential-shape) parameters are determined from the fits. Comparison with potential functions determined after including older mid-IR and visible electronic transition data shows that our analysis of the pure microwave data alone yields potential energy functions that accurately predict (to better than 1%) the overtone vibrational energies far beyond the range spanned by the levels for which the microwave data is available.