Perturbations in the 4ν₃ level of the {\tf="PS7CD9"{\raise7pt\tilde \lower7ptA\clap}^\lower4pt{\hskip-.5pt1}\hskip-1ptA_u} state of acetylene, C₂H₂This article is part of a Special Issue on Spectroscopy at the University of New Brunswick in honour of Colan Linton and Ron Lees.

Abstract

Perturbations in the K = 1 and 3 levels of theà 1 A u ,4 n 3 state of acetylene are explained as interactions with levels of theà 1 A u ,3 1 B 4 (v 3 =1 ,v 4 +v 6 = 4) polyad. A satisfactory least-squares fit to the perturbed level structure has been obtained, treating the 4n 3 state as an asymmetric top perturbed by isolated K = 1 and 3 levels. Accurate deperturbed rotational constants for the interacting states are presented. . Nous obtenons un ajustement satisfaisant par moindres carrés pour la structure des niveaux perturbés, en traitant l'état 4n3 comme une toupie asymétrique perturbée par les niveaux isolés K =1e tK = 3. Nous présentons des valeurs précises libres de perturbation des constantes rotationnelles pour les niveaux en interaction.[Traduit par la Rédaction]

Stretch-bend combination polyads in the Ã1Au state of acetylene, C2H2

“…Included in the data set are two levels, with K"=1 and 3, which are not seen in the jet spectra, but which cause perturbations in the 3 4 level at higher J values; they are described in Ref. [48]. It can be seen that the match between the observed and calculated level positions is very good, with 12 of the 18 observed levels predicted to within 3 cm Confirmation of the K"=1 assignments comes from the asymmetry splittings, where the observed and calculated values of the asymmetry parameter B#C, listed in Table 6, are seen to agree to within about 0.01 cm No attempt has been made to obtain a full least squares fit to the nine interacting vibrational levels, comparable to that in Table 2: the data are by no means as complete, while preliminary fits to the individual polyads show that many correction terms would have to be added to cope with the !…”

Cis-trans isomerization in the S1 state of acetylene: Identification of cis-well vibrational levels

“…The energies of these new levels could not be explained easily in terms of the known fundamental frequencies. To clarify the assignments of these levels we undertook a systematic analysis of the level structure of the 1 A u (S 1 -trans) well [30][31][32][33] using IR-UV double resonance and one-photon fluorescence excitation spectra. The unexpected positions of the new combination levels turned out to result from unusually strong Darling-Dennison resonance between the ν 4 and ν 6 vibrations.…”

James Kay Graham Watson. 20 April 1936—18 December 2020

“…Propynal was the subject of his very first paper (1) as well as five later ones (2, 3, 15, 47, 86). Acetylene (C 2 H 2 ) was the subject of five publications (26, 33, 34, 72, 88), some in collaboration with colleagues in Brussels. The nitric oxide dimer, (NO) 2 , a relatively weakly-bound species, was the subject of six publications (54, 56, 57, 63, 64, 83), which resulted in determination of many of its vibrational and rotational parameters for the first time.…”