The pure rotational spectrum of HPS (X̃¹A′): Chemical bonding in second-row elements

The pure rotational spectrum of HPS, as well as its ³⁴S and D isotopologues, has been recorded at microwave, millimeter, and submillimeter wavelengths, the first observation of this molecule in the gas phase. The data were obtained using a combination of millimeter direct absorption, Fourier transform microwave (FTMW), and microwave-microwave double-resonance techniques, which cover the total frequency range from 15 to 419 GHz. Quantum chemical calculations at the B3LYP and CCSD(T) levels were also performed to aid in spectral identification. HPS was created in the direct absorption experiment from a mixture of elemental phosphorus, H₂S, and Ar carrier gas; DPS was produced by adding D₂. In the FTMW study, these species were generated in a pulsed discharge nozzle from PH₃ and H₂S or D₂S, diluted in neon. The spectra recorded for HPS and its isotopologues exhibit clear asymmetric top patterns indicating bent structures; phosphorus hyperfine splittings were also observed in HPS, but not DPS. Analysis of the data yielded rotation, centrifugal distortion, and phosphorus nuclear spin-rotation parameters for the individual species. The r_m ⁽¹⁾ structure for HPS, calculated from the rotational constants, is r(H-P) = 1.438(1) Å, r(P-S) = 1.9320(1) Å, and θ(H-P-S) = 101.85(9). Empirically correcting for zero-point vibrational effects yields the geometry r_e(H-P) = 1.4321(2) Å, r_e(P-S) = 1.9287(1) Å, and θ_e(H-P-S) = 101.78(1), in close agreement with the r_m⁽¹⁾ structure. A small inertial defect was found for HPS indicating a relatively rigid molecule. Based on these data, the bonding in this species is best represented as H-PS, similar to the first-row analog HNO, as well as HNS and HPO. Therefore, substitution of phosphorus and sulfur for nitrogen and oxygen does not result in a dramatic structural change.