The ν 2 and ν 4 bending fundamentals of phosphine (PH 3 )

The IR absorption spectrum of phosphine (PH3) has been recorded at a resolution of 0.004 cm−1 in the region between 750 and 1400 cm−1. About 2500 rovibrational transitions have been measured and assigned to the ν2 (A1) and ν4 (E) bending fundamentals, including 501 “perturbation allowed” transitions with selection rules Δ(k−l)=±3, ±6, and ±9. Splittings of the K″=3, 6, and 9 lines were observed. Rotational transitions in the vibrationally excited states have also been identified in the far-IR spectra recorded in the past at 0.002 cm−1 resolution between 30 and 200 cm−1 [L. Fusina and M. Carlotti, J. Mol. Spectrosc., 130 (1988) 371]. The rotational structure in the ν2=1 and ν4=1 vibrational states up to J=K=24 was reproduced by fitting simultaneously our experimental data, together with the very accurate transitions previously reported in the literature. The adopted rovibrational Hamiltonian explicitly took into account the Coriolis interaction between the ν2=1 and ν4=1 states, and included also several essential resonances within them. The 46 parameters obtained from the fit reproduced 2736 IR and far-IR transitions retained in the final cycle within the uncertainty of the experimental measurements and 37 microwave and mm-wave transitions with an rms value of 0.9 MHz. The ground state parameters have also been improved by means of ground state combination differences.