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Author: Karl Irikura

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1. To Predict Vibrational Spectra, Are Anharmonic Calculations Worthwhile?
Published: 1/22/2013
Authors: Ruth Lafuente Jacobsen, Karl K Irikura, Russell D Johnson III, Raghu N Kacker
Abstract: Anharmonic calculations using vibrational perturbation theory are known to provide near-spectroscopic accuracy when combined with high-level ab initio potential energy functions. However, performance with economical, popular electronic structure meth ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=911024

2. Electron ionization and gas-phase ion molecule reactions of methylcyclohexane
Published: 11/9/2010
Authors: C. Q. Jiao, Karl K Irikura, S, F Adams, A Garscadden
Abstract: Absolute cross sections for electron impact ionization of methylcyclohexane (MCH, C^d7^H^d14^) are measured as a function of the electron energy in a range of 10 to 200 eV. The reactions between selected hydrocarbon ions with MCH, mainly via hydride ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=906638

3. Thermochemistry of Ammonium Nitrate, NH4NO3, in the Gas Phase
Published: 10/7/2010
Author: Karl K Irikura
Abstract: Hildenbrand and coworkers have shown recently that the vapor above solid ammonium nitrate includes molecules of NH4NO3, not only NH3 and HNO3 as previously believed. Their measurements led to thermochemical values that imply an enthalpy change of D2 ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=905920

4. Scaling Factors and Uncertainties for ab Initio Anharmonic Vibrational Frequencies
Published: 8/21/2009
Authors: Russell D Johnson III, Karl K Irikura, Raghu N Kacker, Ruediger Kessel
Abstract: To predict the vibrational spectra of molecules, ab initio calculations are often used to compute harmonic frequencies, which are usually scaled by empirical factors as an approximate correction for errors in the force constants and for anharmonic ef ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=903585

5. Uncertainties in Scaling Factors for ab Initio Vibrational Zero-Point Energies
Published: 3/21/2009
Authors: Karl K Irikura, Russell D Johnson III, Raghu N Kacker, Ruediger Kessel
Abstract: Vibrational zero-point energies (ZPEs) determined from ab initio calculations are often scaled by empirical factors. An empirical scaling factor partially compensates for the effects arising from vibrational anharmonicity and incomplete treatment of ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=832443

6. in-Adamantane, a Small Inside-Out Molecule
Published: 9/25/2008
Author: Karl K Irikura
Abstract: The hydrocarbon in-adamantane, an adamantane isomer in which one methine hydrogen atom is inside the cage, is predicted by ab initio calculations to be isolable at dry-ice temperature. It is 440 kJ/mol less stable than ordinary adamantane but has a ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=832290

7. Aminoxyl (nitroxyl)Radicals in the Decomposition of RDX
Published: 5/13/2008
Author: Karl K Irikura
Abstract: The explosive RDX (1,3,5-trinitrohexahydro-s-triazine) is thought to decompose by homolytic N-N bond cleavage, among other possible initiation reactions.  Quantum chemistry calculations show that the resulting aminyl radical can abstract an oxyg ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=832241

8. Sigma Stellation: A Design Strategy for Electron Boxes
Published: 1/10/2008
Author: Karl K Irikura
Abstract: The carbon-fluorine antibonding (sigma*) orbitals in a fluorocarbon cage are directed toward a central, common point. If the cage is not too large or too small, the sigma* orbitals will overlap at that point. An added electron can occupy the resulti ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=832005

9. Obtaining Molecular Thermochemistry From Calculations
Published: 9/30/2007
Author: Karl K Irikura
Abstract: There are several computational approaches for predicting gas-phase, molecular thermochemistry. For common organic compounds, empirical methods are quick to compute and have been effectively parameterized. For uncommon compounds, the relative robus ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=831942

10. Experimental Vibrational Zero-Point Energies: Diatomic Molecules
Published: 4/18/2007
Author: Karl K Irikura
Abstract: Vibrational zero-point energies (ZPEs), as determined from published spectroscopic constants, are derived for 85 diatomic molecules. Standard uncertainties are also provided, including estimated contributions from bias as well as the statistical unc ...
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=831982