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Updated: Nov 2, 2025

Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases
Published on: October 29, 2018
Thermochemical Trends in Carbon Chain Molecules HC2H/HC2H (k = 1-6) Studied by Explicitly Correlated CCSD(T)-F12b
Chow-Shing Lam1, Kai-Chung Lau1
1Department of Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
Abstract:
We present a composite procedure based on explicitly correlated CCSD(T)-F12 calculations for accurate energetic predictions for carbon chain molecules HCH encompassing both the even (HC2H) and odd series (HC2H), with the shorter members playing a key role in the evolution of cosmic carbon compounds in both circumstellar envelopes and interstellar medium. This approach considers the contributions of core-valence correlation, scalar relativistic effect, spin-orbit coupling, and zero-point vibrational energy in an additive manner. The computed ionization energies demonstrate outstanding agreement (±0.07 eV) up to a chain size of k = 6 and the literature heats of formation for k ≤ 2 are reproduced with "chemical accuracy" of 1 kcal mol-1. Among the various corrections included, the importance of core-valence correlation effect has been highlighted in the thermochemical calculations for carbon chain growth. The thermochemical trend toward infinite length is also highlighted by extrapolation of ionization energy and triplet-singlet splitting at the CCSD(T) level for k up to 15. The correlation between the end-group effect and the even-odd parity effect observed for HCH chains has been established with the aid of intrinsic bond orbital localization.
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