# Kinetic Laser Absorption Spectroscopy of Vibrationally Excited Hydroxyl Radicals on Infrared Transitions ν = 3 ← 1 and ν = 4 ← 2

## TL;DR

This study uses laser absorption to track the behavior of excited hydroxyl radicals in infrared transitions, revealing their relaxation dynamics and reaction rates.

## Contribution

The paper introduces a novel method for measuring vibrational relaxation kinetics of OH radicals using time-resolved laser absorption.

## Key findings

- The rate constant for OH(ν = 1) relaxation in collisions with water is (9.2 ± 2.0) × 10−12 cm³/s.
- The relative populations of OH(ν = 1) and OH(ν = 2) were determined from the reaction O(1D) + H2O.
- Distinct vibrational relaxation pathways OH(ν = 2) → OH(ν = 1) and OH(ν = 2) → OH(ν = 0) were identified.

## Abstract

The kinetics of vibrationally excited OH(ν = 1) and OH(ν = 2) radicals was studied by time-resolved laser absorption in the overtone IR region. Two DFB laser diodes, 1509.3 and 1589 nm, were used. The technique allowed for the reliable study of the vibrational relaxation kinetics as well as the relative populations of the vibrationally excited states. The yields of OH(ν = 1) and OH(ν = 2) in the reaction O(1D) + H2O were determined. The rate constant of OH(ν = 1) relaxation in collision with water molecules was obtained ((9.2 ± 2.0) × 10−12 cm3/s). The dynamics of OH(ν = 1) and OH(ν = 2) populations were analyzed in detail, which made it possible to separately determine the relative contribution of the vibrational ladder relaxation channels OH(ν = 2) → OH(ν = 1) → OH(ν = 0) and the direct relaxation OH(ν = 2) → OH(ν = 0).