Excited singlet electronic states of acetylene: cis and trans structures and energetics
Molecular electronic structure theory has been used to predict the equilibrium geometries and energies of acetylene in its excited singlet electronic states. A double zeta plus polarization basis set of contracted Gaussian functions was used in conjunction with self-consistent field and large scale configuration interaction wave functions. The first excited singlet state of acetylene is the trans /sup 1/A/sub u/ state, in agreement with the experimental studies of King, Ingold, and Innes. This result is particularly interesting because the lowest triplet state of C/sub 2/H/sub 2/ is not the /sup 3/A/sub u/ state but rather the cis /sup 3/B/sub 2/ state. The predicted geometry of the A /sup 1/A/sub u/ state is r/sub e/(CC)=1.384 A, r/sub e/(CH)=1.096 A, theta/sub e/(HCC)=121.7 /sup 0/, in good agreement with available spectroscopic data. The predicted relative energies of the excited singlet states are 5.06 eV (/sup 1/A/sub u/), 5.54 eV (cis /sup 1/A/sub 2/), 6.87 eV (/sup 1/B/sub 2/), and 7.29 eV (/sup 1/B/sub u/). Thus the energetic ordering of the singlet states is A/sub u/
- Research Organization:
- Department of Chemistry and Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
- OSTI ID:
- 7026751
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 73:11
- Country of Publication:
- United States
- Language:
- English
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