Accurate partition function for acetylene, 12C2H2, and related thermodynamical quantities

Area of Science:

• Chemical Thermodynamics
• Molecular Spectroscopy
• Computational Chemistry

Background:

• Accurate calculation of thermodynamic properties requires precise partition functions.
• Ethyne (acetylene) is a fundamental molecule with applications in various scientific fields.
• Previous calculations may have limitations in scope or accuracy.

Purpose of the Study:

• To compute the internal partition function (Q(int)) of ethyne (C2H2) with high accuracy.
• To provide thermodynamic data for ethyne from 1 K to 2000 K.
• To assess the accuracy of the calculations and discuss potential limitations.

Main Methods:

• Explicit summation of vibration-rotation energy levels up to 15,000 cm(-1).
• Utilizing a global model and constants that reproduce 18,415 literature vibration-rotation lines.
• Performing distinct calculations for para and ortho ethyne species.

Main Results:

• Internal partition function values for ethyne provided from 1 to 2000 K.
• Calculated total internal partition function at 298.15 K is 104.224387(47) or 416.89755(19) depending on nuclear spin conventions.
• Helmholtz function, Gibbs enthalpy function, entropy, and specific heat were also computed.

Conclusions:

• The study provides a comprehensive and accurate dataset for ethyne's thermodynamic properties.
• The accuracy of the partition function calculations is discussed.
• The potential impact of the vinylidene isomer of acetylene on the results is considered.