Density functional theory investigation of physical properties of the OCCN radical and the cation Branko S. Jursic Department of Chemistry, University of New Orleans, New Orleans, LA 70148, USA Received 2 April 1998; accepted 21 July 1998 Abstract Structural and thermodynamic properties for the OCCN radical and its cation were estimated with hybrid, gradient-corrected and local density functional theory methods by using three various Gaussian type basis sets. It was estimated that the radical structure should be a zig-zag structure, which corresponds to the sp 2 hybridization of the carbonyl carbon, while the OCCN cation is linear. The radical ionization potential should be between 8.7 and 9.1 eV with the enthalpy of formation at approxi- mately 51 kcal/mol. It was computed in the infrared spectra that there were two strong absorptions at 1863 and 2080 cm -1 for the CO and the CN functionalities and they should be observable for the OCCN radical.  1999 Elsevier Science B.V. All rights reserved. Keywords: Ionization potential; DFT; Heat of formation; OCCN 1. Introduction There is substantiated speculation that the major channel in the photodissociation of CH 3 C(O)CN is through its alpha cleavage and the formation of the OCCN radical because there is only 35% energy gained through the CN fragmentation [1, 2]. It is very hard to verify the channel formation of the OCCN radical because little is known about its ther- modynamic and spectroscopic properties. To predict the spectroscopic as well thermal properties of the OCCN radical, Francisco and Liu performed a high level of ab initio studies [1]. The constitution of both the OCCN radical and cation suggests that density functional theory methods (DFT) should produce reli- able structural parameter vibrations, as well as ener- gies. Recently, we have demonstrated that DFT methods can accurately compute structures of small polar molecules [3–9], bond dissociation energies [10–15], vibrational spectra [16–18], heats of forma- tion [19–21], ionization potentials [22–24], and elec- tron affinities [25–27]. Here we present a computational study with hybrid, gradient corrected and local DFT methods of struc- tural, spectroscopic and thermal properties of the OCCN radical. To facilitate progress of experimental detection of the OCCN radical, vertical and adiabatic ionization potentials together with vibrational frequencies for the OCCN cation, were also computed. 2. Computational methodology All computational studies were performed with the Gaussian 94 computational package [28]. Three DFT methods that correspond to hybrid, gradient-corrected and local group of DFT methods were used. The Journal of Molecular Structure (Theochem) 460 (1999) 207–212 THEOCH 5808 0166-1280/99/$ - see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0166-1280(98)00318-2