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Search Publications by: Karl K. Irikura (Fed)

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Displaying 1 - 25 of 108

Partial Ionization Cross Sections of Organic Molecules

June 13, 2017
Author(s)
Karl K. Irikura
Partial ionization cross sections are the absolute yields of specific ions from an electron- molecule collision. They are necessary for modeling plasmas and for determining the sensitivity of mass spectrometers, among other applications. One mass

To Predict Vibrational Spectra, Are Anharmonic Calculations Worthwhile?

January 22, 2013
Author(s)
Ruth L. Jacobsen, Karl K. Irikura, Russell D. Johnson III, Raghu N. Kacker
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 methods is

Electron ionization and gas-phase ion molecule reactions of methylcyclohexane

November 9, 2010
Author(s)
C. Q. Jiao, Karl Irikura, S, F. Adams, A Garscadden
Absolute cross sections for electron impact ionization of methylcyclohexane (MCH, C 7H 14) 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 transfer

Thermochemistry of Ammonium Nitrate, NH4NO3, in the Gas Phase

October 7, 2010
Author(s)
Karl K. Irikura
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 D298 = 98

Scaling Factors and Uncertainties for ab Initio Anharmonic Vibrational Frequencies

August 21, 2009
Author(s)
Russell D. Johnson III, Karl K. Irikura, Raghu N. Kacker, Ruediger Kessel
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 effects

Uncertainties in Scaling Factors for ab Initio Vibrational Zero-Point Energies

March 21, 2009
Author(s)
Karl K. Irikura, Russell D. Johnson III, Raghu N. Kacker, Ruediger Kessel
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

How Good Are Force Fields for Gas-Phase Protonated Peptides?

October 16, 2008
Author(s)
Christopher Kinsinger, Karl K. Irikura
With the increase in mass-spectrometry-based proteomics, many research projects depend on the chemistry of peptide fragmentation. Elucidating fragmentation mechanisms requires a thorough exploration of the potential energy surface. Conformational searching

in-Adamantane, a Small Inside-Out Molecule

September 25, 2008
Author(s)
Karl K. Irikura
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 barrier

Aminoxyl (nitroxyl)Radicals in the Decomposition of RDX

May 13, 2008
Author(s)
Karl K. Irikura
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 oxygen atom from

Sigma Stellation: A Design Strategy for Electron Boxes

January 10, 2008
Author(s)
Karl K. Irikura
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 resulting