Chapter 7 - Molecular laser-induced breakdown spectroscopy

Abstract

This chapter focuses on molecular laser-induced breakdown spectroscopy (LIBS). Of interest are applications in diverse fields that include plasma diagnostics, combustion diagnostics, molecular plasma spectroscopy, and selected astrophysics spectra analyses. Laser ablation molecular isotopic spectrometry (LAMIS) reveals favorable measurement opportunities for identification of atomic isotope compared to direct isotope spectroscopy. For selected molecules of different atomic isotope composition, or for isotopologues, the presented summary discusses LAMIS advantages. LIBS experiments convey formation of diatomic molecules primarily due to recombination. The analysis of diatomic emission spectra reveals excitation temperatures up to 10kK following laser-induced optical breakdown. Cyanide (CN), aluminum monoxide (AlO), titanium monoxide, Swan bands of C2, and hydroxyl molecules are frequently recorded in nanosecond LIBS investigations over and above the usual atomic emission spectra. The CN molecule occurs within the first few hundred nanoseconds after optical breakdown, and Abel inversion of CN line-of-sight data determines the spatial distributions of molecular signals. For nanosecond LIBS, expansion dynamics and shockwave phenomena explain the measured radial distributions for CN and also for hydrogen. Chemical equilibrium distribution computations assess deviation from thermodynamic equilibrium. This chapter also communicates measurements of AlO ablation spectra and associated analysis with line strength data. Analysis of astrophysics C2 Swan spectra provides further challenges, but in turn can serve as a gauge for chemical analysis with molecular LIBS.