ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The electronic structures of the ground and lowest lying excited state of the silicon methylidyne radical (HCSi) have been investigated at the self-consistent field, configuration interaction with single and double excitations, coupled cluster with single and double excitations (CCSD), and CCSD including a perturbative expansion for connected triples CCSD(T) levels of theory with a wide range of basis sets. The total energies and physical properties including equilibrium geometries, dipole moments, harmonic vibrational frequencies, and Renner–Teller splitting are reported. At our highest level of theory [CCSD(T)/cc-pVQZ], the ground electronic state (X˜ 2Π) has a linear geometry with re(CH)=1.0781 Å and re(CSi)=1.6956 Å. This is in good agreement with the experimental values of r0(CH)=1.0677 Å and r0(CSi)=1.6925 Å, respectively. In the A˜ 2Σ+ state, HCSi is also found to have a linear geometry with re(CH)=1.0737 Å and re(CSi)=1.6130 Å at the [CCSD(T)/cc-pVQZ] level, confirming experimental values of r0(CH)=1.0625 Å, r0(CSi)=1.6118 Å, and the observation of C–Si triple bond character. With the same method, the X˜ 2Π and A˜ 2Σ+ state C–H stretching vibrational frequencies are predicted to be 3271 and 3319 cm−1, respectively, for which experimental values are not available. The classical X˜–A˜ splitting (Te value) was determined to be 32.6 kcal/mol (1.41 eV, 11 730 cm−1) and quantum mechanical splitting (T0 value) to be 33.5 kcal/mol (1.45 eV, 11726 cm−1), which are in excellent agreement with the experimental T0 value of 11 766.721 cm−1 (33.64 kcal/mol, 1.459 eV). The linear excited A˜ 2Σ+ state of the molecule has a real degenerate bending vibrational frequency, whereas the ground state (X˜ 2Π) is subject to the Renner–Teller effect and presents two distinct real vibrational frequencies. The Renner parameter (ε) and average harmonic bending frequency (ω2) of the X˜ 2Π state are predicted to be ε=−0.114 and ω2=518 cm−1 at the CCSD(T)/cc-pVQZ level of theory. The electronic structure analysis of the ground state showed that the HCSi radical is an A-type Renner–Teller molecule. © 2001 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1345512
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