Determination of anharmonicity constants from the Raman spectrum of gaseous acetylene

Abstract

From an analysis of the photoelectrically recorded Raman band of acetylene at 3950 cm-', which contains contributions from u, +u4 and its hot bands, u3+us in Fermi resonance with u2+u4+2vg, and the Q-branch of 215, some anharmonicity constants were determined. In particular xZ2 = -7.4 cm-' was obtained directly for the first time, other constants are revised due to a more complete consideration of the resonance perturbations. A computer simulation of the u4 fundamental and the u1 +u4 combination band shows excellent agreement with the experimental spectra.

Quartic anharmonic resonances in acetylenes and haloacetylenes

“…may be sensitive to the relative signs of eigenvector elements. The observed value of K 3,245 for 12 C 2 H 2 has been rather precisely determined by several different groups [1][2][3][4][5] who are all in close agreement; the value given in Table VI, Ϯ18.28 ͑5͒ cm Ϫ1 , is an average. 23 The calculated value of Ϫ48.13 cm Ϫ1 from the Strey and Mills force field is at first disappointingly different.…”

“…[2][3][4][5][6][7] There is a similar resonance between the symmetric C-H stretching fundamental 1 and the combination band 2 ϩ2 5 , which is only a weak resonance in 12 C 2 H 2 where the bands are 48 cm Ϫ1 apart, but becomes a strong resonance in 13 C 2 H 2 where the corresponding wave functions are again almost 50/50 mixed. 8,9 Turning to substituted acetylenes, Borro, Mills, and Mose 10 have recently reported a resonance between 1 and 2 ϩ2 4 in both monofluoroacetylene HCCF and monochloroacetylene HCCCl, although in both cases the resonance is relatively weak.…”

“…͑Some authors have previously denoted the resonance coefficient with a lower case k, with four subscripts, creating the misleading impression that the only contribution to the resonance is the corresponding term from the quartic anharmonic force field.͒ We use a comma to separate quanta created from quanta annihilated in order to avoid the ambiguity to which Lehmann drew attention, that in the absence of a separator symbols such as K rstu might suggest a resonance between either r ϩ s and t ϩ u , or r and s ϩ t ϩ u , which would have different theoretical expressions. Thus, for example, the coefficient for the resonance in acetylene which has previously been denoted either K 2345 or k 2345 is here denoted K 3,245 .…”

The Raman spectrum of toluene vapour

“…As is known' in the case of CH,N02 and CH,BF2, the apparent degeneracy of methyl vibrations is lifted in the vapour phase. In the Raman spectrum of liquid toluene only one broad band is observed at 1441 cm-', and both of the two methyl bending modes ~2 3 and ~3 2 are assigned to this value. However, if this degeneracy is split in the vapour spectra and if we assume by analogy with nitromethane that the out-of-plane deformation mode ~3 2 is moved to higher wavenumbers than the inplane deformation mode ~2 3 , we can estimate their positions from Fig.…”

Precision Measurements of Acetylene Spectra at 1.4–1.7 μm Recorded with 352.5-m Pathlength

“…objections to this are reinforced by the work of Finsterhölzl et al (28). The alternate assignment proposed by Smith and…”