The photoinduced hydrogen elimination reaction in phenol via the conical intersections of the dissociative ${}^1\pi {\sigma }^{*}$ state with the ${}^1\pi {\pi }^{*}$ state and the electronic ground state has been investigated by time-dependent quantum wave-packet calculations. A model including three intersecting electronic potential-energy surfaces ($S_0$ , ${}^1\pi {\sigma }^{*}$ , and ${}^1\pi {\pi }^{*}$ ) and two nuclear degrees of freedom (OH stretching and OH torsion) has been constructed on the basis of accurate ab initio multireference electronic-structure data. The electronic population transfer processes at the conical intersections, the branching ratio between the two dissociation channels, and their dependence on the initial vibrational levels have been investigated by photoexciting phenol from different vibrational levels of its ground electronic state. The nonadiabatic transitions between the excited states and the ground state occur on a time scale of a few tens of femtoseconds if the ${}^1\pi {\pi }^{*}\text{‐}{}^1\pi {\sigma }^{*}$ conical intersection is directly accessible, which requires the excitation of at least one quantum of the OH stretching mode in the ${}^1\pi {\pi }^{*}$ state. It is shown that the node structure, which is imposed on the nuclear wave packet by the initial preparation as well as by the transition through the first conical intersection $\left({}^1\pi {\pi }^{*}\text{‐}{}^1\pi {\sigma }^{*}\right)$ , has a profound effect on the nonadiabatic dynamics at the second conical intersection $\left({}^1\pi {\sigma }^{*}\text{‐}{S}_0\right)$ . These findings suggest that laser control of the photodissociation of phenol via IR mode-specific excitation of vibrational levels in the electronic ground state should be possible.

We present a new two-step uncontracted spin-orbit configuration interaction (CI) method which automatically accounts for spin-orbit polarization effects on multiconfigurational wave functions by selecting the single excitations having a significant spin-orbit interaction with a chosen determinantal reference space. This approach is in the line of a conventional two-step method, as a sophisticated correlation treatment in a scalar relativistic approximation is carried out in the first step. In the second step, we define a model space which includes a set of reference configurations able to represent all the wanted states along with singly excited configurations selected with the spin-orbit (SO) operator. We then exploit the first-step calculation in order to include correlation effects via an effective Hamiltonian technique and diagonalize the full matrix on the determinantal basis. The method combines the advantages of both one-step and conventional two-step SO–CI methods; it intends to treat efficiently the cases where both relativity and extended CI treatments are needed. The new code EPCISO is tested on the spin-orbit splitting of the ${}^{2}P$ electronic ground state of the thallium atom which, in spite of its very simple electronic structure is a well-known difficult case study for SO–CI methods. The EPCISO code yields results in excellent agreement with the experimental splitting value; they are compared to those obtained using the conventional two-step CIPSO code.