Thermodynamics of Helium-4 Dimerization and Trimerization.

Area of Science:

• Low-temperature physics
• Quantum fluids
• Chemical thermodynamics

Background:

• Understanding the behavior of helium-4 at low temperatures is crucial for condensed matter physics.
• The formation of helium clusters (dimers and trimers) influences the macroscopic properties of the fluid.

Purpose of the Study:

• To determine the equilibrium thermochemical properties of helium-4 dimerization and trimerization.
• To investigate the populations of helium-4 dimers and trimers at temperatures between 3.0 and 10.0 K.

Main Methods:

• Utilized a new equation of state (EOS) for helium-4.
• Calculated equilibrium constants (K_P^o), standard enthalpy, and standard entropy changes.
• Performed statistical thermodynamic calculations for comparison.

Main Results:

• Appreciable populations of helium-4 dimers (⁴He₂) and trimers (⁴He₃) exist at sufficiently low temperatures.
• At 3.0 K, K_P^o values for dimerization and trimerization are 0.4832 and 0.4876, respectively.
• Standard enthalpy changes at 3.0 K were -54.53 J/mol for dimerization and -110.0 J/mol for trimerization.

Conclusions:

• The new EOS accurately models helium-4 cluster formation.
• Calculations considering only monomer, dimer, and trimer provide valuable insights into low-temperature helium behavior.
• Statistical thermodynamic results align qualitatively with EOS predictions.