High Temperature Optical Spectra of Diatomic Molecules at Local Thermodynamic Equilibrium
Institute of Physics, 10000 Zagreb, Croatia
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Atoms 2018, 6(4), 67; https://doi.org/10.3390/atoms6040067
Received: 31 October 2018
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Revised: 23 November 2018
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Accepted: 27 November 2018
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Published: 30 November 2018
In the paper, several theoretical approaches to the determination of the reduced absorption and emission coefficients under local thermodynamic equilibrium conditions were exposed and discussed. The full quantum-mechanical procedure based on the Fourier grid Hamiltonian method was numerically robust but time consuming. In that method, all transitions between the bound, free, and quasi-bound states were treated as bound–bound transitions. The semi-classical method assumed continuous energies of ro-vibrational states, so it did not give the ro-vibrational structure of the molecular bands. That approach neglected the effects of turning points but agreed with the averaged-out quantum-mechanical spectra and it was computer time efficient. In the semi-quantum approximation, summing over the rotational quantum number J was done analytically using the classical Franck–Condon principle and the stationary–phase approximation and its consumption of computer time was lower by a few orders of magnitude than the case of the full quantum-mechanical approach. The approximation described well the vibrational but not the rotational structure of the molecular bands. All the above methods were compared and discussed in the case of a visible and near infrared spectrum of LiHe, Li2, and Cs2 molecules in the high temperature range.
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Keywords:
diatomic molecules; optical spectra; thermodynamic equilibrium; quantum-mechanical calculation; semi-classical approximation
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MDPI and ACS Style
Beuc, R.; Movre, M.; Pichler, G. High Temperature Optical Spectra of Diatomic Molecules at Local Thermodynamic Equilibrium. Atoms 2018, 6, 67. https://doi.org/10.3390/atoms6040067
AMA Style
Beuc R, Movre M, Pichler G. High Temperature Optical Spectra of Diatomic Molecules at Local Thermodynamic Equilibrium. Atoms. 2018; 6(4):67. https://doi.org/10.3390/atoms6040067
Chicago/Turabian StyleBeuc, Robert, Mladen Movre, and Goran Pichler. 2018. "High Temperature Optical Spectra of Diatomic Molecules at Local Thermodynamic Equilibrium" Atoms 6, no. 4: 67. https://doi.org/10.3390/atoms6040067
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