Effect of Vibrational Pre-Excitation on the Dissociation Dynamics of HOD²⁺

Abstract

Preferential breaking of chemical bonds using few-cycle, intense laser pulse to obtain desired products offer a formidable challenge in understanding ultrafast chemical reactivity. In a recent study [J. Chem. Phys. 2015, 143, 244310], it was found that carrier-envelope phase influences the bond-selective fragmentation in HOD with up to 3-fold enhancement. We present a detailed theoretical study to understand the influence of initial vibrational states governing the dissociation dynamics. We have carried out a time-dependent quantum mechanical wave packet study on the ground electronic state (X̃ (3)B1) of HOD(2+). Analytical potential energy surface for the ground electronic states of both the neutral molecule and dication has been developed at multireference configuration interaction level of theory with aug-cc-pVQZ basis set. Branching ratio is computed from the accumulated flux in H(+) + OD(+) and D(+) + OH(+) dissociation channels. Our investigation demonstrate a strong dependency on the initial conditions, and thereby preferential cleavage of bonds can be achieved. We have also compared our results with experimental and other theoretical studies.

Hydrogen migration within a water molecule: formation of HD+upon irradiation of HOD with intense, ultrashort laser pulses

“…We attempt to rationalize these observations in terms of quantum chemical information about neutral and ionized HOD. Recently, ground state potential energy surfaces of HOD, HOD + and HOD 2+ were obtained by numerically solving the time-dependent Born-Oppenheimer Schrödinger equation in internal (bond-length, bond-angle) coordinates [22,33]. The HOD molecule was modelled in these studies with two degrees of freedom and a bending angle of 104.45 ;…”

Non-resonant vibrational excitation of HOD and selective bond breaking

“…The photodissociation dynamics of HOD under the influence of 2-cycle, non-resonant laser pulses is studied by numerically solving the time-dependent Schrödinger equation in internal coordinates. 12,31 Since the stretching and bending modes are only weakly coupled, a two degree of freedom model is considered where O-H and O-D bond stretchings are allowed and the bending is neglected. 7 The kinetic energy operator can be written aŝ…”

Controlling Chemical Reactions with Laser Pulses

“…While solving the time-dependent Schrödinger equation, it is always advantageous to separate the faster electronic motion from the slower nuclear motion, based on the Born–Oppenheimer approximation. This so-called adiabatic separation enables us to visualize a molecule as a set of nuclei moving on the instantaneous eigenstate, namely, the potential energy surface 9 provided by the electrons. The gradients occurring on the potential energy surface quantify the forces acting on the atoms and molecules during a chemical transformation.…”

“…Therefore, understanding and simulating vibrational energy flow on a molecular level with essential knowledge of the intramolecular couplings between different modes is of utmost importance and is a prerequisite to achieving the desired chemical transformation via modeselective vibrational excitation. In special cases, when the molecular vibrations are largely independent, an easier way to promote the reaction to a particular product channel is by supplying energy to specific degrees of freedom of the reactant molecule (e.g., in the form of vibrational pre-excitation using laser light 8,9 ). The recent availability of ultrashort, intense laser pulses comprising a few wave cycles has introduced a new parameter of importancethe carrier envelope phase (CEP) defined as the temporal offset between the maxima of the pulse envelope and the optical cycle.…”