title: On the HCN - HNC Energy Difference.
abstract: The value for the HCN → HNC 0 K isomerization energy has been investigated by combining state-of-the-art electronic structure methods with the Active Thermochemical Tables (ATcT) approach. The directly computed energy difference between HCN and HNC at the HEAT-456QP level of theory is 5236 ± 50 cm(-1). This is substantially lower (by ∼470 cm(-1) or ∼1.3 kcal/mol) than the recently proposed high-level multireference configuration interaction value of 5705 ± 20 cm(-1) of Barber et al. ( Mon. Not. R. Astron. Soc. 2014, 437, 1828-1835 ). The discrepancy was analyzed by the ATcT approach, using several distinct steps, which (a) independently corroborated the current single-reference HEAT-456QP result, (b) independently found that the recent multireference-based value is highly unlikely to be correct within its originally stated uncertainty, and (c) produced a recommended value of 5212 ± 30 cm(-1) for the HCN → HNC isomerization energy at 0 K, based on all currently available knowledge. The ATcT standard enthalpies of formation at 0 and 298 K for HCN, HNC, and their cations and anions are also presented.
authors.affiliation: Institute for Theoretical Chemistry, Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Thanh L
authors.initials: TL
authors.lastname: Nguyen
authors.affiliation: Institute for Theoretical Chemistry, Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Joshua H
authors.initials: JH
authors.lastname: Baraban
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.|Computation Institute, The University of Chicago , Chicago, Illinois 60637, United States.
authors.forename: Branko
authors.initials: B
authors.lastname: Ruscic
authors.affiliation: Institute for Theoretical Chemistry, Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: John F
authors.initials: JF
authors.lastname: Stanton