Analysis of time-resolved superposed atomic hydrogen Balmer lines and molecular diatomic carbon spectra

Abstract

We present analysis of superposition spectra following laser-induced breakdown (LIB) of methane. Both hydrogen-beta and hydrogen-gamma lines contain discernible contributions from diatomic carbon emissions for time delays of 1 to 2 μs from pulsed, 8 ns, infrared Nd:YAG laser radiation LIB. Analysis of the atomic lines and molecular C(2) spectra reveal electron and molecular excitation temperatures of typically 13,000 and 5000 K, respectively.

Atomic and molecular emissions in laser-induced breakdown spectroscopy

“…17 and 18 indicate clearly the presence of C 2 molecular emissions for a time delay of Δτ = 2.1 μs. Temperature inferred from the fitting of the C 2 "fingerprints" revealed molecular temperatures in the range of 4000-6000 K [22,23]. The H β profile at a time delay of and temporally resolved imaging appears to be a necessary experimental approach for the purpose of further investigating the indicated temperature difference.…”

“…19, shows overview spectra. The Δv = + 2 band of the Swan system is seen in the H γ emission following LIB in expanding methane [22,23]. Non-linear fitting routines are applied to determine the molecular temperature of the C 2 contribution to the measured atomic H β and H γ lines.…”

“…Laser-induced micro-plasma that contains carbon usually shows spectroscopic signatures of the diatomic molecular Swan system [22,23,74]. For the LIB experiments in expanding methane, these molecular C 2 "fingerprints" are discernible for time delays on the order of 1 to 2 μs, see Fig.…”

“…Molecular data can be found in Herzberg's works; however, frequently accurate databases are required for analytic studies that have become available recently, e.g., for select transitions of diatomic molecules of interest that include diatomic CN, C 2 , AlO molecular transitions [15][16][17][18] amongst other diatomic molecules. Recently, detailed C 2 [19][20][21][22][23][24], Titanium Monoxide TiO [25][26][27] spectra including a study of femto-second versus nano-second laser ablation [28], and AlO emission spectra of the B 2 Σ + → X 2 Σ + [29,30] transition were communicated. Temperature information is determined using Boltzmann plot techniques for atomic and/or molecular transitions [19,21,[31][32][33] combined with accurate computation of diatomic molecular spectra [20,21,34].…”

Computation of diatomic molecular spectra for selected transitions of aluminum monoxide, cyanide, diatomic carbon, and titanium monoxide

“…Equally, the programs SPECAIR and LIFBASE focus on various aspects of computing molecular spectra. For analysis of superposition spectra of hydrogen Balmer series hydrogen-beta and hydrogen-gamma lines [23], our C 2 line strength data are preferred after the computed spectra were compared [23] with the ones obtained by use of SPECAIR. Our C 2 carbon Swan line strength data nicely agree with recently published work [24].…”