Selective bond dissociation of HOD molecule by optimally designed polychromatic IR+UV pulse: a genetic-algorithm-based study

ABSTRACT

A theoretical investigation of selective bond dissociation of O–H or O–D bond of HOD molecule is carried out by optimally designed electromagnetic field where optimisation is performed by Genetic Algorithm (GA). Two strategies depending upon the objective function and variable space for optimisation have been followed to achieve selective photodissociation. In Strategy I flux along a particular channel (J _{H + O-D}/J _{D + O-H}) in the repulsive excited state of HOD is considered in defining the objective function with a polychromatic IR pulse of eight components and a UV radiation of two components being optimally found out by GA. The polychromatic IR pulse distributes the population among the low quanta vibrational states of O–H or O–D stretching mode in ground electronic state and the subsequent UV pulse transfers the population to the excited state where photodissociation occurs. According to the direction of population along O–H or O–D stretch in ground electronic state, fluxes in the channels may be expected. We have obtained a maximum value of 92.38% and 74.12% along J _{H + O-D} and J _{D + O-H} channels, respectively. The Strategy II is the conventional strategy of selective vibrational excitation followed by population transfer to excited state by single UV pulse. In this case, the polychromatic IR fields are optimised by GA to achieve selective vibrational excitation on |1, 0⟩, |2, 0⟩, |0, 1⟩ and |0, 2⟩ states and the matching single UV pulse is fired for electronic excitation. The first two states correspond to the O–H stretch and population transfer from these states to excited state result in predominant flux along H+O–D channel and similar scheme from the last two states result in D+O–H dissociation as they are effectively of O–D character. The best values of J _{H + O-D} and J _{D + O-H} are 86.91% and 65.94% obtained by using Strategy II.

KEYWORDS:

• Optimal control
• selective dissociation
• genetic algorithm
• pulse design

Acknowledgments

S. Talukder would like to thank Indian Association for the Cultivation of Science for granting research fellowship. P. Chaudhury and S. Adhikari acknowledge UGC for the funding through Major Research Project.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

UGC.