Sub 20 cm-1 computational prediction of the CH bond energy - a case of systematic error in computational thermochemistry

James H Thorpe; David Feller; David H Bross; Branko Ruscic; John F Stanton

doi:10.1039/d2cp03964h

Sub 20 cm^-1 computational prediction of the CH bond energy - a case of systematic error in computational thermochemistry

Phys Chem Chem Phys. 2023 Aug 16;25(32):21162-21172. doi: 10.1039/d2cp03964h.

Authors

James H Thorpe¹, David Feller^{2

3}, David H Bross⁴, Branko Ruscic⁴, John F Stanton¹

Affiliations

¹ The Quantum Theory Project, Department of Chemistry, University of Florida, Gainesville, Florida, 32611, USA. johnstanton@chem.ufl.edu.
² Washington State University, Pullman, Washington 99164-4630, USA.
³ University of Alabama, Tuscaloosa, Alabama 35487-0336, USA.
⁴ Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, USA. ruscic@anl.gov.

PMID: 36200428
DOI: 10.1039/d2cp03964h

Abstract

The bond dissociation energy of methylidyne, D₀(CH), is studied using an improved version of the High-Accuracy Extrapolated ab initio Thermochemistry (HEAT) approach as well as the Feller-Peterson-Dixon (FPD) model chemistry. These calculations, which include basis sets up to nonuple (aug-cc-pCV9Z) quality, are expected to be capable of providing results substantially more accurate than the ca. 1 kJ mol^-1 level that is characteristic of standard high-accuracy protocols for computational thermochemistry. The calculated 0 K CH bond energy (27 954 ± 15 cm^-1 for HEAT and 27 956 ± 15 cm^-1 for FPD), along with equivalent treatments of the CH ionization energy and the CH⁺ dissociation energy (85 829 ± 15 cm^-1 and 32 946 ± 15 cm^-1, respectively), were compared to the existing benchmarks from Active Thermochemical Tables (ATcT), uncovering an unexpected difference for D₀(CH). This has prompted a detailed reexamination of the provenance of the corresponding ATcT benchmark, allowing the discovery and subsequent correction of a systematic error present in several published high-level calculations, ultimately yielding an amended ATcT benchmark for D₀(CH). Finally, the current theoretical results were added to the ATcT Thermochemical Network, producing refined ATcT estimates of 27 957.3 ± 6.0 cm^-1 for D₀(CH), 32 946.7 ± 0.6 cm^-1 for D₀(CH⁺), and 85 831.0 ± 6.0 cm^-1 for IE(CH).