Equilibrium Thermodynamics of the Dimers and Trimers of H₂ and D₂ and Their Heterodimer (H₂)(D₂)

Abstract

The equilibrium thermochemical properties of the dimers and trimers of H 2 and D 2 are obtained from the equations of state (EOSs) of normal H 2 and D 2 . The standard dimer and trimer equilibrium constants K D o and K T o and ΔH D, T o and ΔS D, T o are reported for these weakly bound van der Waals molecules between 25 and 45 K. Statistical thermodynamics (ST) calculations of H 2 and D 2 dimerization using Morse pair potentials to account for intermolecular interactions, obtained from recent experimental work, are in qualitative agreement with the EOS results. The entropies of the H 2 and D 2 dimers and trimers are calculated from the EOS ΔS o values and ST calculations of the monomer entropies.

Thermodynamic Properties of van der Waals Dimers and Trimers of Nonpolar Gases and Their Correlation with Lennard-Jones Potential Well Depths

“…For the rare gas dimers, quasi-bound rotational levels were included in the summations. These calculations, which have been reported before, − are applied in the present work to the dimers at the respective 0.7 T c temperatures. The last column of Table contains the results of these calculations.…”

“…In four recent publications, the equilibrium thermodynamic properties of the dimers and trimers of five rare gases helium to xenon, , as well as H 2 , D 2 , CO 2 , and CH 4 , were reported. In the present work, such calculations are applied to these nine species, as well as to other nonpolar gases, CF 4 , ethane, ethene, SF 6 , propane, and 2,2-dimethylpropane (neopentane).…”

“…The dimer and trimer equilibria considered in this article pertain to the following processes 2 normalM ⇌ normalD 0.25em K normalD normalo 0.25em and 0.25em 3 normalM ⇌ normalT 0.25em K normalT normalo where M, D, and T refer to monomer, dimer, and trimer and K D o and K T o are the respective standard equilibrium constants. These constants are obtained using a method described previously. − It utilizes an accurate equation of state (EOS) of the gas and its implementation in the PC application Reference Fluid Thermodynamic and Transport Properties Database (REFPROP)…”

Thermodynamics of the van der Waals Dimers of O2, N2 and the Heterodimer (N2)(O2) and Their Presence in Earth’s Atmosphere

“…Although a number of studies have been reported concerning the nature of the interactions between the components, few have dealt with the equilibrium thermodynamic properties of van der Waals dimers and trimers. In recent publications, such information has been obtained from the equation of state (EOS) of the rare gases He – Xe and for 10 nonpolar molecules ranging from H 2 to C­(CH 3 ) 4 . − Since the thermodynamic properties of heterodimer formation cannot be obtained from the EOS-based method that can be employed for the homodimers, we sought an approach that could be applied to all three dimers, (N 2 )­(N 2 ), (O 2 )­(O 2 ), and (N 2 )­(O 2 ). Such calculations would provide consistency to the results thus obtained.…”