High-resolution FTIR study of the ν1+ν2 combination band of PF3 around 1380 cm-1

Thr nu(1) + nu(2) (A(1), 1377.75 cm(-1)) parallel combination band of PF3 has been studied with high resolution (4.4 X 10(-3) cm(-1)) This band was found to be isolated in the spectrum and provided 1794 infrared transitions assigned with J(max) = 52 and K-max = 43. A perturbation-free model gave a standard deviation (sd) of 0.96 x 10(-3) cm(-1) for 1457 non zero-weighted lines with the J-dependent parameters slightly differing from those expected from nu(1) and nu(2) fundamental bands. A model including the Coriolis interaction with the upper levels of the unobserved nu(2) + nu(3) (E, 1345.44 cm(-1)) band reduced the sd to 0.55 X 10(-3) cm(-1) and improved the nu(1) + nu(2) parameters, In this fit, we had to constrain almost all nu(2) + nu(3) parameters to the values obtained from the results of the nu(2) and nu(3) fundamental bands including the coupling terms, not only those of the Coriolis but also those of the l(2,2) and l(2, - 1) resonances connecting the two l sublevels of nu(2) + nu(3)(+/-1). The Fermi resonance linking the upper levels of nu(2) + nu(3) and 2 nu(2) + nu(4) (E, 1321.44 cm(-1)) has to be taken into account in order to determine x(23) = - 2.175 cm(-1) while the anharmonic constant x(12) = -1.9025 cm(-1) has been directly obtained. The presently available anharmonic constants of PF3 are compiled and some of them are used to explain two observed hot band features. (C) 2000 Elsevier Science B.V, All rights reserved.