High-Resolution FTIR Study of the (nu3 + nu4, nu1 + nu4) Interacting System of Rovibrational Bands of PF3 Between 1100 and 1300 cm-1.

With a resolution of 4.4 x 10(-3) cm-1, we were able to identify in this range the very weak nu2 + 2nu04 (A1) component near 1180 cm-1, the nu3 + nu4 band around 1205 cm-1 with its (A1 + A2) and E very intermixed components, and the nu1 + nu4 (E) band centered at 1238 cm-1. Three thousand six hundred transitions belonging to the (nu3 + nu4, nu1 + nu4) interacting system were fitted together with a model taking into account l(2, 2) interactions inside nu1 + nu4 and between (A1 + A2) and E components of nu3 + nu4, the l-vibrational resonance inside nu3 + nu4(A1 + A2), and the Coriolis interactions between nu1 + nu4 and nu3 + nu4(A1 + A2) on one hand and between nu1 + nu4 and nu3 + nu4 (E) on the other. Four available MW transitions were also included in the fit. A rms of 0.76 x 10(-3) cm-1 was obtained with 34 free parameters among 38. Normally the Fermi resonance, which links nu3 to nu2 + nu4 with a coupling term W234 = 2.86 cm-1, must connect each component of nu3 + nu4 with each component of nu2 + 2nu4. But since we have only little experimental information about the weak nu2 + 2nu04 component (120 assigned lines) and none about the dark nu2 + 2nu+/-24 component, it was not possible to introduce this resonance in the fit. However, the bandcenters' shifts were calculated since the basic coupling term W234 and the anharmonic constant x24 are well known. Therefore, according to this approximation, the very sensitive anharmonic constants x34 and g34 could be deduced. Of course the x14 Fermi-independent constant, derived directly from the (nu1 + nu4)0 bandcenter given by the fit, was certainly more accurate. Copyright 1998 Academic Press.