Mass-independent Dunham analysis of the known electronic states of platinum sulfide, PtS, and analysis of the electronic field-shift effect

Several new vibrational bands of the [12.5] Omega = 0(+)-X-3 Sigma(-)(+)(Omega=0) and the [15.9] B Omega = 0(+)-X-3 Sigma(-)(+)(Omega=0) transitions have been observed in high resolution absorption measurements recorded using Intracavity Laser Spectroscopy (ILS). These new bands have been rotationally analyzed and incorporated into a comprehensive PtS dataset that was fit to a mass-independent Dunham expression using PGOPHER. The comprehensive dataset included all reported field-free, gas phase spectroscopic data for PtS, including 32 Fourier transform microwave transitions (estimated accuracy: 1 kHz), 9 microwave/optical double resonance transitions (25 kHz), 51 millimeter and submillimeter transitions (25-50 kHz), 469 molecular beam-laser induced fluorescence transitions (0.003 cm(-1)), and 4870 ILS transitions (0.005 cm(-1)). The determined equilibrium constants have been used with the Rydberg-Klein-Rees method to produce potential energy curves for the four known electronic states of PtS. Isotopic shifts in electronic transition energy beyond expectations from the Born-Oppenheimer approximation were observed and treated as electronic field-shift effects due to the difference in the nuclear charge radius between Pt isotopes. The magnitude and sign of the determined field-shift parameters are rationalized through the analysis of the previously reported ab initio calculations.