Acetylene: Synergy between theory and experiment

Journal Article · Tue Jun 01 00:00:00 EDT 1993 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.464496· OSTI ID:6585744

Lundberg, J K; Field, R W ^[1]; Sherrill, C D; Seidl, E T; Xie, Y; Schaefer, III, H F ^[2]

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1. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
2. Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602 (United States)

Six anomalous vibronic feature states [[similar to]2 cm[sup [minus]1] full-width at half-maximum (FWHM), each consisting of [similar to]20 partially resolved eigenstates] have been observed in stimulated emission pumping (SEP) spectra of C[sub 2]D[sub 2]. Of the two plausible assignments for these features, the one most consistent with spectroscopic observations would imply that the lowest energy [ital cis]-bent triplet state of acetylene has [ital T][sub 0][le]25 820 cm[sup [minus]1], which is inconsistent with previous [ital ab] [ital initio] predictions. New higher level [ital ab] [ital initio] quantum mechanical methods have been used to predict the energy difference between [ital [tilde X]] [sup 1][Sigma][sub [ital g]][sup +] ground state and the [ital cis]-bent [ital [tilde a]] [sup 3][ital B][sub 2] lowest triplet state of acetylene. In conjunction with a triple zeta plus double polarization plus [ital f] function (TZ2P[ital f]) basis set, the coupled cluster including single, double, and linearized triple excitations CCSD(T) method yields [ital T][sub 0]=[Delta][ital E]([ital [tilde a]] [sup 3][ital B][sub 2]--[ital [tilde X]] [sup 1][Sigma][sub [ital g]][sup +])=30 500 cm[sup [minus]1]. The true value of [ital T][sub 0] for the [ital [tilde a]] [sup 3][ital B][sub 2] state is estimated to be [similar to]500 cm[sup [minus]1] higher. At the same level of theory the zero-point levels of the lowest triplet state of the [ital trans]-bent ([ital [tilde a]] [sup 3][ital B][sub [ital u]]) and vinylidene ([ital [tilde a]] [sup 3][ital B][sub 2]) isomers lie at still higher energies. This result conclusively rules out any triplet assignment for the anomalous feature states.

• DOE Contract Number: FG09-87ER13811; FG02-87ER13671
• OSTI ID: 6585744
• Journal Information: Journal of Chemical Physics; (United States), Vol. 98:11; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ACETYLENE
ELECTRON SPECTRA
EIGENSTATES
OPTICAL PUMPING
RESOLUTION
STIMULATED EMISSION
TRIPLETS
ALKYNES
EMISSION
ENERGY-LEVEL TRANSITIONS
HYDROCARBONS
MULTIPLETS
ORGANIC COMPOUNDS
PUMPING
SPECTRA
664200* - Spectra of Atoms & Molecules & their Interactions with Photons- (1992-)