Spin-orbit calculations of the molecular states of CH 3I +, related to photofragmentation experiments

Abstract

The molecular states of CH 3I + have been calculated by means of the CIPSI method. The spin-orbit coupling of iodine is introduced through an effective Hamiltonian and with pseudo-potentials (CIPSO algorithm). We present results for the twelve first E 1 2 states and six first E 3 2 states of CH 3I + which dissociate into the fragments CH 3( 2A″ 2) and I + ( 3P, 1D, 1S) or CH 3 + ( 1A′ 1) and I( 2P). At the equilibrium geometry of the neutral molecule ( r CI = 2.14 Å) the 1 E 1 2 , 2 E 1 2 and 5 E 1 2 states are the X̃ 2E 1 2 , Ã 2A 1 and B̃ 2E states, as known in photoelectron spectroscopy. These states present a binding region around 2.14 Å (1 E 1 2 ), 2.7 Å (2 E 1 2 ) and 3.2 Å (5 E 1 2 ). Dissociation energy is given with an error of 0.3 eV for the 1 E 1 2 state (and 1 E 3 2 state). The 5 E 1 2 state presents a well of 0.33 eV while it is repulsive without spin-orbit coupling. The 1 E 1 2 and 2 E 1 2 states are those between which the photon absorption takes place in the photodissociation experiments. Our calculations show that the spin-orbit coupling between these states is less than 2% at 2.14 Å in excellent agreement with the spectroscopic results; over 3.5 Å it increases rapidly with the C-I internuclear distance. We have calculated the dipole moment of the 2 E 1 2 ←1 E 1 2 transition and the anisotropy parameter β of the angular distribution of the photofragments. These results are in good agreement with the experimental ones.