Kinetics and dynamics measured using IntraCavity Laser Absorption Spectroscopy

Abstract

IntraCavity Laser Absorption Spectroscopy (ICLAS) is a high-resolution, high sensitivity spectroscopic method capable of measuring line positions, linewidths, lineshapes, and absolute line intensities with a sensitivity that far exceeds that of a traditional multiple pass absorption cell or Fourier Transform spectrometer. From the fundamental knowledge obtained through these measurements, information about the underlying spectroscopy, dynamics, and kinetics of the species interrogated can be derived. The construction of an ICLA Spectrometer will be detailed, and the measurements utilizing ICLAS will be discussed, as well as the theory of operation and modifications of the experimental apparatus. Results include: i) Line intensities and collision-broadening coefficients of the A band of oxygen and previously unobserved, high J, rotational transitions of the A band, hot-band transitions, and transitions of isotopically substituted species. ii) High-resolution (0.013 cm-1) spectra of the second overtone of the OH stretch of trans-nitrous acid recorded between 10,230 and 10,350 cm-1. The spectra were analyzed to yield a complete set of rotational parameters and an absolute band intensity, and two groups of anharmonic perturbations were observed and analyzed. These findings are discussed in the context of the contribution of overtone-mediated processes to OH radical production in the lower atmosphere.

(cont.) iii) The implementation of Correlated Double Sampling (CDS) for time-resolved studies of CN fragments generated by the excimer laser photolysis of acrylonitrile. iv) The extension of ICLAS to study the kinetics of a test system. Nitrosyl hydride, HNO, was reacted with oxygen in a flow cell, and the subsequent chemistry was monitored using an electronic transition of HNO. Analysis of the rate equations and time integrated measured signal yielded a preliminary value for the rate constant of the reaction, HNO + 02 [right arrow] products.