High-resolution FTIR study of the nu(1)+nu(2) combination band of PF3 around 1380 cm(-1)

Thr nu(1) + nu(2) (A(1), 1377.75 cm(-1)) parallel combination band of PF3 h as been studied with high resolution (4.4 X 10(-3) cm(-1)) This band was fo und to be isolated in the spectrum and provided 1794 infrared transitions a ssigned with J(max) = 52 and K-max = 43. A perturbation-free model gave a standard deviation (sd) of 0.96 x 10(-3) c m(-1) for 1457 non zero-weighted lines with the J-dependent parameters slig htly differing from those expected from nu(1) and nu(2) fundamental bands. A model including the Coriolis interaction with the upper levels of the uno bserved 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 t o 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 couplin g 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). T he 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 determin e 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 o f them are used to explain two observed hot band features. (C) 2000 Elsevie r Science B.V, All rights reserved.