Abstract
In this work, we calculate the partition functions and thermodynamic quantities of molecular hydrogen isotopologues using the rovibrational energy levels provided by the highly accurate ab initio adiabatic potential energy functions recently determined by Pachucki and Komasa (Pachucki, K.; Komasa, J. J. Chem. Phys.2014, 141, 224103). The partition functions are calculated by including all bound energy levels of the isotopologues, up to their dissociation limits, plus the quasi-bound levels lying below the centrifugal potential barriers. For the homonuclear isotopologues, H2, D2, and T2, we also determine the partition functions and thermodynamic quantities of the normal mixtures using the statistical treatment recently proposed by Colonna et al. (Colonna, G.; D’Angola, A.; Capitelli, M. Int. J. Hydrogen Energy2012, 37, 9656) based on the definition of the partition function of the mixture, which avoids inconsistencies in the values of the thermodynamic quantities depending directly on the internal partition function, in the high-temperature limit.
Highlights
There is no doubt that molecular hydrogen is one of the chemicals of the moment
By a number of authors,[19,26,27,30] it is convenient to include the quasi-bound rovibrational energy levels in the partition functions, especially those lying between the dissociation limit of the isotopologue and the maximum of the centrifugal potential barrier generated by the effective internuclear potential for values of J ≠ 0.40 we have recalculated variationally the bound energy levels of the Pachucki and Komasa adiabatic potentials, and further determined variationally the quasi-bound energy levels
We have calculated the partition functions and thermodynamic quantities of the six isotopologues of molecular hydrogen, H2, HD, HT, D2, DT, and T2, using the ro-vibrational energy levels extracted from the adiabatic potentials recently determined by Pachucki and Komasa employing high-level ab initio methods.[34]
Summary
There is no doubt that molecular hydrogen is one of the chemicals of the moment. Not surprisingly, it is a key player in the energy transition as an energy storage and transport vector, and as an alternative fuel,[1−5] and plays an important role in atmospheric and interstellar chemistry.[6−15] It is essential to accurately characterize their thermodynamic properties, including all their isotopologues.[16,17]. We accurately calculate the partition functions and thermodynamic quantities of the six isotopologues of molecular hydrogen in the temperature range from 1 to 10000 K For this purpose, we use the adiabatic potentials of the isotopologues recently determined by Pachucki and Komasa using high-level ab initio methods.[34,35] Pachucki and Komasa provided the rovibrational bound energy levels of all isotopologues, up to their dissociation limits, which can be used directly to obtain the partition functions as sums of the exponential energy factors over all the levels. We have determined the partition functions and thermodynamic quantities of the normal mixtures of the homonuclear isotopologues H2, D2, and T2, using the rigorous statistical thermodynamic formulation recently developed by Colonna et al.,[30] which eliminates inconsistencies in the values of thermodynamic quantities depending directly on the partition functions, such as the entropy and the Gibbs free energy, when compared to the equilibrium values at high temperatures
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