title: Toward accurate thermochemistry of the (24)MgH, (25)MgH, and (26)MgH molecules at elevated temperatures: corrections due to unbound states.
abstract: The total partition functions QT and their first two moments Q(')T and Q(″)T, together with the isobaric heat capacities CpT, 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 QT 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 CpT, 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 (24)MgH, (25)MgH, and (26)MgH 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.
authors.affiliation: MTA-ELTE Research Group on Complex Chemical Systems, P.O. Box 32, H-1518 Budapest 112, Hungary.
authors.forename: Tamás
authors.initials: T
authors.lastname: Szidarovszky
authors.affiliation: MTA-ELTE Research Group on Complex Chemical Systems, P.O. Box 32, H-1518 Budapest 112, Hungary.
authors.forename: Attila G
authors.initials: AG
authors.lastname: Császár