부산대학교 도서관

The photodissociation processes of CH2 into CH and H have been studied using ab initio multireference configuration-interaction methods. Two-dimensional potential energy surfaces of the ten lowest triplet states correlating with the seven lowest states of CH have been calculated as functions of bond angle and one C–H bond distance, keeping the other C–H distance fixed at the equilibrium CH2 value. Transition dipole moments connecting the excited states with the ground state have been obtained as well. It is shown that efficient photodissociation of CH2 into CH (X 2Π)+H can occur by absorption from the ground X 3B1 (1 3A‘) state into the 1 3A1 (1 3A’) state at about 6.3 eV. Photodissociation into excited CH (a 4Σ-)+H can take place through the 1 3A2 (2 3A‘) and 2 3B1 (3 3A‘) states, although in a more complex manner since several avoided crossings occur along the reaction path. The 1 3A2 state is a so-called low-angle state, which has an equilibrium bond angle of less than 60° and correlates directly with C(3P)+H2. At 180°, when the molecule has D∞h or C∞v symmetry, interesting crossings between the ground and low-lying surfaces are found. Altogether, these crossings and correlations are predicted to lead to complicated dissociation dynamics for most of the states. The higher-lying states of CH2 can photodissociate either directly into excited states of CH, or they can be predissociated by the repulsive 1 5A2 (1 5A‘) state, which correlates with CH (a 4Σ-)+H. [ABSTRACT FROM AUTHOR]