# Preparing Superposition States to Modify the Spectra and to Achieve Complete Selectivity in Photodissociation Reactions

## TL;DR

This paper shows how to use superposition states to control and enhance chemical reactions with high selectivity using light pulses.

## Contribution

A new geometric optimization methodology is introduced to prepare superposition states for complete selectivity in photodissociation reactions.

## Key findings

- Using weak ultrashort pulses, reaction efficiency toward desired products can be increased by 100–200%.
- High selectivity can be achieved by suppressing the most dominant reaction channel to less than one part in a million.
- Preparing superpositions of vibrational states allows precise control over reaction outcomes.

## Abstract

We derive and apply the geometric optimization methodology
to modify
the photodissociation spectra of CH3I in the A band. For
this purpose, we prepare optimized initial wave functions that maximally
exploit interference-induced coherent control to drive a reaction
mediated by nonadiabatic couplings in a polyatomic molecule essentially
from the beginning. By designing functionals that maximize the output
of the products, or that imply competition between the products, or
discrimination of one of them, we test the performance of the methods
and the effect of preparing initial vibrational coherences among CH3–I stretching vibrational states, CH3 vibrational
states, or both. Our results show that using weak ultrashort pulses,
one can easily increase the efficiency of the reaction toward any
of the products by 100–200% using vibrational states related
to the reaction coordinate; that one can increase the efficiency by
more than 100% and at the same time almost completely quench the output
of products in the other channels. Finally, if one demands high selectivity
in the reaction, we show that it is possible to suppress even the
most dominant channel to less than one part in a million by preparing
superpositions of all available vibrational states optimized with
the proper functional.