ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
High-level coupled-cluster theory with large basis sets was used to determine the optimized geometries and harmonic vibrational frequencies for the ground and low-lying excited electronic states of the CH2N and CH2P radicals. Additionally, isotropic hyperfine splitting constants were determined for the C2v CH2X, trans-HCXH and cis-HCXH (where X=N and P) isomers as a gauge of the delocalization of the unpaired electron. The geometrical parameters of X˜ 2B2 CH2X, the trans-HCXH and cis-HCXH conformers, and the first three excited states are reported at the coupled-cluster level with single, double, and perturbatively applied triple excitations [CCSD(T)] using Dunning's correlation consistent polarized valence quadruple-ζ basis set (cc-pVQZ). The C2v structures on the ground state surface are predicted to lie 9.3 and 13.5 kcal/mol lower than the trans- and cis-isomers, respectively, for CH2N and 28.1 and 30.0 kcal/mol, respectively, for CH2P. There are many other important properties of CH2N and CH2P which are not known from experiment. The geometrical parameters of the CH2N ground state [r(C–N)=1.2462 Å, r(C–H)=1.0921 Å, and θ(HCH)=119.4°] and the CH2P ground state [r(C–P)=1.6583 Å, r(C–H)=1.0842 Å, and θ(HCH)=118.9°] agree well with the C–N and C–P bond distances of the r0 structures derived from microwave data, although notable differences were observed in the C–H bond distance and HCH bond angle. This research resolves an earlier discrepancy between theory and experiment for the ground state C–P distance in CH2P. The Fermi contact terms for 1H, 13C, 14N, and 31P were determined at CCSD(T) level of theory with the cc-pVTZ and cc-pVQZ basis sets and are in reasonable agreement with the experimental values with a maximum deviation of 26 MHz for CH2N and 11 MHz for CH2P. The excited states of CH2N are predicted to lie 33 000 cm−1 (A˜ 2B1), 36 000 cm−1 (B˜ 2A′), and 38 000 cm−1 (C˜ 2A1) above the ground state, and the excited states of CH2P to lie approximately 21 000 cm−1 (A˜ 2A′), 26 000 cm−1 (B˜ 2B1), and 33 000 cm−1 (C˜ 2A1) above the ground state. © 2001 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1337062
