Electronically excited and ionized states of the CH 2 CH 2 OH radical:A theoretical study

• Published in: The Journal of chemical physics 2010-03, Vol.132 (11), p.114308-114308-8
• Main Authors: Karpichev, B., Koziol, L., Diri, K., Reisler, H., Krylov, A. I.
• Format: Article
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.3354975

The low lying excited electronic states of the 2-hydroxyethyl radical, CH 2 CH 2 OH , have been investigated theoretically in the range 5-7 eV by using coupled-cluster and equation-of-motion coupled-cluster methods. Both dissociation and isomerization pathways are identified. On the ground electronic potential energy surface, two stable conformers and six saddle points at energies below ∼ 900   cm − 1 are characterized. Vertical excitation energies and oscillator strengths for the lowest-lying excited valence state and the 3s, 3 p x , 3 p y , and 3 p z Rydberg states have been calculated and it is predicted that the absorption spectrum at ∼ 270 - 200   nm should be featureless. The stable conformers and saddle points differ primarily in their two dihedral coordinates, labeled d HOCC (OH torsion around CO), and d OCCH ( CH 2 torsion around CC). Vertical ionization from the ground-state conformers and saddle points leads to an unstable structure of the open-chain CH 2 CH 2 OH + cation. The ion isomerizes promptly either to the 1-hydroxyethyl ion, CH 3 CHOH + , or to the cyclic oxirane ion, CH 2 ( OH ) CH 2 + , and the Rydberg states are expected to display a similar behavior. The isomerization pathway depends on the d OCCH angle in the ground state. The lowest valence state is repulsive and its dissociation along the CC, CO, and CH bonds, which leads to CH 2 + CH 2 OH , CH 2 CH 2 + OH , and H + CH 2 CHOH , should be prompt. The branching ratio among these channels depends sensitively on the dihedral angles. Surface crossings among Rydberg and valence states and with the ground state are likely to affect dissociation as well. It is concluded that the proximity of several low-lying excited electronic states, which can either dissociate directly or via isomerization and predissociation pathways, would give rise to prompt dissociation leading to several simultaneous dissociation channels.