Energy diagram for ground electronic state dissociation and isomerization of hydroxymethyl radical. All energies are relative to CH2OH (CD2OH) vibrational ground state and calculated at RCCSD(T)/CBS level of theory using RCCSD(T)/AVTZ harmonic zero-point energies. For a quantitative comparison with the most recent experimental measurements of dissociation energies the ZPEs of CH2OH (CD2OH) and its dissociation products are calculated also using VSCF/VCI. These values are given in parentheses. Corresponding imaginary frequencies are indicated below the barriers. Note the lower barrier for dissociation of CH3O relative to CH2OH, and the comparable barriers for OH bond fission and isomerization in CH2OH.
RCCSD(T)/AVTZ geometries for relevant stationary points of the CH2OH PES. All structures, except the CH2OH minimum (a), have C s symmetry. Bond lengths are in angstroms, dihedral angles are shown in square brackets. CH2O parameters: r CO = 1.208 Å, r CH = 1.102 Å, ∠COH = 121.7°.
Contour plot showing the potential energy as a function of the OH bond length and the HOCH' dihedral angle (that equals 22° at the equilibrium geometry, (1)) with all other degrees of freedom relaxed. Dissociation without relaxation of the indicated torsional angle, (2), results in a barrier almost 4000 cm−1 above the saddle point, (3). Energy increases from blue to red and orange, interval between countor lines is 1000 cm−1.
Frontier MOs (SOMO, HOMO-1, and HOMO-2) at the selected geometries of Fig. 3: equilibrium (a), a structure with the stretched OH bond and the HOCH' angle fixed at the equilibrium value (b), and the TS (c).
CH2OH spectroscopic parameters and zero-point energies (in cm−1) from VCI calculations. Vibrational mode descriptions are approximate; the mixed states in CH2OH are denoted by leading contributions in their VCI wavefunctions.
CD2OH spectroscopic parameters and zero-point energies (in cm−1) from VCI calculations.
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