The nu(2) and nu(4) bending fundamentals of phosphine (PH3)

The IR absorption spectrum of phosphine (PH3) has been recorded at a resolu tion 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 v(2) (A(1) ) and v(4) (E) bending fundamentals, including 501 "perturbation allowed" t ransitions with selection rules Delta (k - l) = +/- 3, +/- 6, and +/- 9. Sp littings of the K" = 3, 6, and 9 lines were observed. Rotational transition s 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 2 00 cm(-1) [L. Fusina and M. Carlotti, J. Mol. Spectrosc, 130 (1988) 371]. T he rotational structure in the v(2) = 1 and v(4) = 1 vibrational states up to J = K = 24 was reproduced by fitting simultaneously our experimental dat a, together with the very accurate transitions previously reported in the l iterature. The adopted rovibrational Hamiltonian explicitly took into accou nt the Coriolis interaction between the v(2) = 1 and v(4) = 1 states, and i ncluded also several essential resonances within them. The 46 parameters ob tained from the fit reproduced 2736 IR and far-IR transitions retained in t he 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 grou nd stare parameters have also been improved by means of ground state combin ation differences; (C) 2000 Elsevier Science B.V. All rights reserved.