Accurate ab initio potential energy curves and spectroscopic properties of the four lowest singlet states of C₂

Journal Article · Sat Dec 07 00:00:00 EST 2013 · Theoretical Chemistry Accounts

DOI:https://doi.org/10.1007/s00214-013-1425-x· OSTI ID:1134285

Boschen, Jeffery S. ^[1]; Theis, Daniel ^[1]; Ruedenberg, Klaus ^[1]; Windus, Theresa L. ^[1]

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1. Ames Laboratory (AMES), Ames, IA (United States)

The diatomic carbon molecule has a complex electronic structure with a large number of low-lying electronic excited states. In this work, the potential energy curves (PECs) of the four lowest lying singlet states (X-1 Sigma(+)(g), A(1)Pi(u), B-1 Delta(g), and B'(1)Sigma(+)(g)) were obtained by high-level ab initio calculations. Valence electron correlation was accounted for by the correlation energy extrapolation by intrinsic scaling (CEEIS) method. Additional corrections to the PECs included core-valence correlation and relativistic effects. Spin-orbit corrections were found to be insignificant. The impact of using dynamically weighted reference wave functions in conjunction with CEEIS was examined and found to give indistinguishable results from the even weighted method. The PECs showed multiple curve crossings due to the B-1 Delta(g) state as well as an avoided crossing between the two (1)Sigma(+)(g) states. Vibrational energy levels were computed for each of the four electronic states, as well as rotational constants and spectroscopic parameters. Comparison between the theoretical and experimental results showed excellent agreement overall. Equilibrium bond distances are reproduced to within 0.05 %. The dissociation energies of the states agree with experiment to within similar to 0.5 kcal/mol, achieving "chemical accuracy." Vibrational energy levels show average deviations of similar to 20 cm(-1) or less. The B-1 Delta(g) state shows the best agreement with a mean absolute deviation of 2.41 cm(-1). Calculated rotational constants exhibit very good agreement with experiment, as do the spectroscopic constants.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC02-07CH11358
• OSTI ID: 1134285
• Report Number(s): IS-J-8224
• Journal Information: Theoretical Chemistry Accounts, Vol. 133, Issue 2; ISSN 1432-881X
• Publisher: Springer
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
Ab initio electronic structure
c2
configuration interaction
configuration-interaction
correlated calculations
COUPLED-CLUSTER
Diatomic carbon
dissociation
gaussian-basis sets
ground-state
infrared bands
molecular electronic wavefunctions
MOLECULE
Multi-configurational wave functions
MULTIREFERENCE
nitrogen molecule
phillips system
spectroscopic properties