Overtone-induced dissociation and isomerization dynamics of the c radical (CH2OH and CD2OH).
Part I: A theoretical study.
E. Kamarchik, C.P. Rodrigo, J.M. Bowman, H. Reisler, and A.I. Krylov
J. Chem. Phys. 136, 084304
The dissociation of the hydroxymethyl radical, CH2OH,
and its isotopolog,
CD2OH, following the excitation of high OH stretch overtones is studied by
quasi-classical molecular dynamics calculations using a global potential
energy surface (PES) fitted to ab initio calculations. The PES includes
CH2OH and CH3O minima, dissociation products, and all relevant barriers.
Its analysis shows that the transition states for OH bond fission and
isomerization are both very close in energy to the excited vibrational
levels reached in recent experiments and involve significant geometry changes
relative to the CH2OH equilibrium structure. The energies of key stationary
points are refined using high-level electronic structure calculations.
Vibrational energies and wave functions are computed by coupled anharmonic
They show that high OH-stretch overtones are mixed with other modes.
Consequently, trajectory calculations carried out at energies about 3000 cm-1
above the barriers reveal that
despite initial excitation of the OH stretch, the direct OH bond bond fission is relatively slow (10 ps)
and a considerable fraction of the radicals undergoes isomerization to
the metoxy radical.
The computed dissociation energies are:
D0(CH2OH -> CH2O + H)=10,188 cm-1,
D0(CD2OH -> CD2O + H)=10,167 cm-1,
D0(CD2OH -> CHDO + D)=10,787 cm-1.
All are in excellent agreement with the experimental results. For
CH2OH, the barriers for the direct OH bond fission and isomerization are:
14,205 and 13,839 cm-1, respectively.
Download this paper (PDF, NaN kB)
Computational studies of electronically excited and open-shell species: Jahn-Teller systems, radicals, diradicals and triradicals