Toward accurate thermochemistry of the 24MgH, 25MgH, and 26MgH molecules at elevated temperatures

Corrections due to unbound states

Tamás Szidarovszky, A. Császár

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13 Citations (Scopus)

Abstract

The total partition functions Q T and their first two moments Q ′ T and Q ″ T, together with the isobaric heat capacities C p T, are computed a priori for three major MgH isotopologues on the temperature range of T = 100-3000 K using the recent highly accurate potential energy curve, spin-rotation, and non-adiabatic correction functions of Henderson et al. [J. Phys. Chem. A 117, 13373 (2013)]. Nuclear motion computations are carried out on the ground electronic state to determine the (ro)vibrational energy levels and the scattering phase shifts. The effect of resonance states is found to be significant above about 1000 K and it increases with temperature. Even very short-lived states, due to their relatively large number, have significant contributions to Q T at elevated temperatures. The contribution of scattering states is around one fourth of that of resonance states but opposite in sign. Uncertainty estimates are given for the possible error sources, suggesting that all computed thermochemical properties have an accuracy better than 0.005% up to 1200 K. Between 1200 and 2500 K, the uncertainties can rise to around 0.1%, while between 2500 K and 3000 K, a further increase to 0.5% might be observed for Q ″ T and C p T, principally due to the neglect of excited electronic states. The accurate thermochemical data determined are presented in the supplementary material for the three isotopologues of 24MgH, 25MgH, and 26MgH at 1 K increments. These data, which differ significantly from older standard data, should prove useful for astronomical models incorporating thermodynamic properties of these species.

Original languageEnglish
Article number014103
JournalThe Journal of Chemical Physics
Volume142
Issue number1
DOIs
Publication statusPublished - Jan 7 2015

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Thermochemistry
thermochemistry
Electronic states
astronomical models
Molecules
Scattering
thermochemical properties
molecules
Potential energy
scattering
electronics
Phase shift
Temperature
Electron energy levels
Specific heat
temperature
partitions
phase shift
Thermodynamic properties
thermodynamic properties

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

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title = "Toward accurate thermochemistry of the 24MgH, 25MgH, and 26MgH molecules at elevated temperatures: Corrections due to unbound states",
abstract = "The total partition functions Q T and their first two moments Q ′ T and Q ″ T, together with the isobaric heat capacities C p T, are computed a priori for three major MgH isotopologues on the temperature range of T = 100-3000 K using the recent highly accurate potential energy curve, spin-rotation, and non-adiabatic correction functions of Henderson et al. [J. Phys. Chem. A 117, 13373 (2013)]. Nuclear motion computations are carried out on the ground electronic state to determine the (ro)vibrational energy levels and the scattering phase shifts. The effect of resonance states is found to be significant above about 1000 K and it increases with temperature. Even very short-lived states, due to their relatively large number, have significant contributions to Q T at elevated temperatures. The contribution of scattering states is around one fourth of that of resonance states but opposite in sign. Uncertainty estimates are given for the possible error sources, suggesting that all computed thermochemical properties have an accuracy better than 0.005{\%} up to 1200 K. Between 1200 and 2500 K, the uncertainties can rise to around 0.1{\%}, while between 2500 K and 3000 K, a further increase to 0.5{\%} might be observed for Q ″ T and C p T, principally due to the neglect of excited electronic states. The accurate thermochemical data determined are presented in the supplementary material for the three isotopologues of 24MgH, 25MgH, and 26MgH at 1 K increments. These data, which differ significantly from older standard data, should prove useful for astronomical models incorporating thermodynamic properties of these species.",
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