Analysis of infrared spectra of gaseous TIF

Abstract

Vibration–rotational spectra of 205Tl19F and 203Tl19F in the electronic ground state X0+ were measured in absorption in the range of wave number [Formula: see text] with diode lasers as spectral sources. Analysis of all available data yielded values of coefficients of radial functions for the potential energy and other molecular properties; only eight independently fitted and two constrained parameters sufficed to reproduce satisfactorily and with physical meaning the frequencies and wave numbers of about 890 distinct pure rotational and vibration–rotational transitions. Independent of nuclear mass, the equilibrium internuclear separation Re of TlF is (2.084 3517 ± 0.000 0039) × 10−10 m; the maximum range of validity of radial functions is 1.85 ≤ R/10−10 m ≤ 2.45. Comparing these results with those of InF, we attribute the large magnitude of [Formula: see text] to the finite and isotopically varying nuclear volume of Tl rather than to (adiabatic) effects of nuclear mass, whereas no such effect is detectable for In in InF. Other aspects of nonadiabatic effects for these polar molecules TlF and InF are discussed.