EQUILIBRIUM GEOMETRY OF THE HCCN TRIPLET GROUND-STATE - CARBENE OR ALLENE - AN OPEN-SHELL COUPLED CLUSTER STUDY INCLUDING CONNECTED TRIPLE EXCITATIONS

被引:71
作者
SEIDL, ET
SCHAEFER, HF
机构
[1] Center for Computational Quantum Chemistry, University of Georgia, Athens
关键词
D O I
10.1063/1.462836
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The molecular structure of the HCCN molecule has been investigated using open-shell coupled cluster methods. The full single and double excitation procedure (CCSD) is used initially. Connected triple excitations were then included perturbatively via the CCSD(T) method. A standard doubel zeta plus polarization (DZP) basis set, designated H(41p/2s1p), C,N(9s5p1d/4s2p1d), was used initially. The predicted carbene H-C-C equilibrium bond angles are 133.8-degrees (CISD), 138.4-degrees (CCSD), and 139.8-degrees with the CCSD(T) method. The corresponding bent-linear energy differences are 5.30, 2.70, and 2.15 kcal/mol, respectively. A much larger basis set was chosen to consider the importance of d functions on hydrogen and f functions on the carbon and nitrogen atoms. Using this H(5s2p1d/3s2p1d), C,N(10s6p2d1f/5s3p2d1f) basis, the H-C-C equilibrium bond angle is 136.3-degrees with the CISD method and the bent-linear energy difference 3.8 kcal/mol. Best estimates of the HCC equilibrium bond angle and singlet-triplet separation are 142-degrees and 0.8 kcal/mol, respectively. The relationship of these theoretical results to several experiments is discussed.
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页码:4449 / 4452
页数:4
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