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In order to describe correctly the
complicated nature of the nuclear motion in the CH2OH
radical a dynamic model of CH2OH was developed.
The strong structural flexibility due to the out-of-plane
motions and the appreciable anharmonicity along some in-plane
vibrational modes were taken into consideration (Windows Media, 81Kb).
The dynamic problem was done separately for
the out-of-plane and in-plane vibrational modes in a basis set of
harmonic oscillator eigenfunctions. Potential energy surfaces dependent
on displacements of all nine internal coordinates from their
equilibrium values in the planar structure of Cs symmetry
were built using the energies of 1793 geometries of CH2OH.
Computations were done with correlation-consistent polarized valence
basis sets of triple zeta quality and at the second (MP2) and fourth
(MP4) orders of many body perturbation theory, and by the coupled
cluster singles and doubles method with perturbative treatment of
triple excitations [CCSD(T)]. The equilibrium geometry and energy
parameters were extrapolated to the complete basis set limit. IR
intensities of the lowest excitations were estimated by calculation of
matrix elements of the dipole moment for the corresponding transitions.
The vibrationally averaged values of the geometric parameters of CH2OH
were computed. The results obtained were found to be in good agreement
with available experimental data. The heat of formation of CH2OH (at 298.15 K), -17.0 +/- 0.7 kJ/mol, was calculated by a study of the CH2OH ==> CH2O + H reaction using the augmented basis set of quintuple-z quality and the relativistic and core-valence corrections of the total energies. The partition functions of CH2OH were calculated by the explicit summation of vibrational and rotational levels. Some structural and thermodynamics properties of CH2O are reported also. |
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