Potential High Energy Density Materials Research Articles

New potential high-energy materials: Oxadiaziridine, N 2H 2O. High-level calculations

A recent suggestion that oxadiaziridine, N 2H 2O, might act as a potential high-energy density material prompts us to determine the enthalpies of formation and combustion of the two conformational isomers of this compound. As a fundamental measure of the reactivity of N 2H 2O, the proton affinity of both isomers was also determined. Gaussian-2, Gaussian-3, and two complete basis set methods were used.

Are Four Oxygens Enough to Stabilize the N8 Cube? Dissociation Pathways of Cage Isomers of N8O4.

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Are Four Oxygens Enough to Stabilize the N8 Cube? Dissociation Pathways of Cage Isomers of N8O4

Various all-nitrogen molecules have been examined as candidates for high energy density materials (HEDM), because of the energy release that would accompany the dissociation of such a molecule down to N2 molecules. Numerous molecules Nx have been shown to dissociate too easily to be a viable HEDM, including small Nx all-nitrogen cages. One possible solution to the instability of small Nx cages is oxygen insertion into the N−N bonds. Conversion of N−N bonds into N−O−N bonding groups would relieve much of the ring strain in small Nx cages, thereby stabilizing the molecule and possibly making the NxOy molecule a good HEDM. Several cage isomers of N8O4 are examined by theoretical calculations to evaluate their suitability as potential HEDM. Calculations are carried out with Hartree−Fock theory and Moller−Plesset perturbation theory (MP3 and MP4), using the CC-PVDZ basis set of Dunning. The relative thermodynamic stability of the isomers is discussed, along with dissociation energies for the various N8O4 cages.

Ab Initio Calculations on the (1)2Δ Excited State and Low-Lying Quartet States of Ga·N2: Simulation of Its LIF Spectrum

The (2)Delta and (4)Sigma (-) excited states of Ga .N-2, which were assigned by Ellis et al. (Phys. Chem. Chem. Phys. 1999, 1, 2709) to the upper states of two LIF transitions observed from the Ga .N-2 (X) over tilde (2)Pi State with onsets of 33468 and 37633 cm(-1), respectively, have been studied by high-level ab initio calculations. Minimum-energy geometrical parameters, harmonic vibrational frequencies, and relative energies were computed at the SERHF, CASSCF, B3LYP, MP2, QCISD, and CCSD(T) levels of calculation, using standard and specifically designed, all-electron and ECP (for Ga) basis sets of up to aug-cc-pVQZ quality. In addition, the low-lying linear (4)Pi and a number of T-shaped quartet states of Ga .N-2 were also studied. Franck-Condon factors (FCFs) of selected electronic transitions were calculated. Absorption spectra were simulated by employing the computed FCFs. On the basis of ab initio results and spectral simulations, the assignment of the 33468 cm(-1) LIF band is concluded to be the (2)Delta (3/2) 200 cm(-1)). In addition, all low-lying Ga .N-2 quartet states considered were found to be either very weakly bound van der Waals states (Ga-N bond length ca. 5 Angstrom) or well-bound charge transfer states, and none of them can be assigned to the upper state of this LIF band. Doubts concerning the identity of the molecular carrier and the electronic states involved in this LIF band remain. Finally, the stabilities of the charge-transfer quartet states of Ga .N-2 investigated in this work have been rationalized in terms of bonding interaction between the HOMOs of Ga and the LUMOs of N-2 and electrostatic attraction resulting from charge transfer from Ga to N-2. Possible applications of this kind of bonding and charge-transfer interactions in an M .N-4 ring system have been discussed briefly in relation to stabilizing an N-n system, where M .N-n represents a potential high energy density material.

Theoretical study of the N10 clusters without double bonds

Quantum chemical ab initio methods have been used to examine nine N10 clusters without double bonds. In additional to the three N10 isomers previously studied in the literature, six new N10 structures were investigated. Fully geometry optimization, harmonic vibrational frequency, and thermodynamics calculation of nine different N10 molecules were performed at the RHF/6-31G*, B3LYP/6-31G*, and MP2/6-31G* levels. All of the nine structures were found to be local minima on the energy hypersurface at the RHF/6-31G* level, whereas eight structures are stable at the B3LYP/6-31G* level. At the MP2/6-31G* level, seven local minima were found. They would be potential high-energy density material (HEDM). According to the results presented herein, the structure N10[V(C2v)] is the most stable molecule of all the N10 clusters without double bonds. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 34–43, 2001

Is there a transition state for the unimolecular dissociation of cyclotetraoxygen (O4)?

The cyclo-O4 molecule is isoelectronic with cyclobutane and has been mentioned as a potential new high energy density material (HEDM). The important unresolved question has been whether or not cyclo-O4 is a genuine minimum on the O4 potential energy hypersurface. Here the transition state for cyclo-O4 dissociation to two O2 molecules has been located at a number of levels of theory using a double zeta plus polarization (DZP) basis set. The theoretical methods with which the transition state geometry was optimized include two-configuration self-consistent-field (TCSCF), configuration interaction including all single and double excitations (CISD), coupled cluster including all single and double excitations (CCSD), and the latter with a noniterative correction for connected triple excitations, CCSD(T). The equilibrium geometry of O4 has D2d symmetry, while a stationary point of D2 symmetry is of Hessian index two (i.e., two imaginary vibrational frequencies) at the highest level of theory, DZP CCSD(T). The true transition state lies only slightly lower energetically (classical barrier 7.9 kcal/mole) and is of C2 symmetry with the DZP CCSD(T) method. The activation energy was predicted in a completely consistent manner to be 6.2 kcal/mole. The possibility that this barrier could disappear entirely at higher levels of theory is discussed. It is concluded that the O4 barrier is too low for O4 to be useful as a HEDM.

Potential new high energy density materials: Cyclooctaoxygen O8, including comparisons with the well-known cyclo-S8 molecule

The cyclic O8 molecule has been studied using ab initio quantum mechanical methods. Molecular structures were fully optimized at levels of theory up to and including second-order perturbation theory (MP2) using a double zeta plus polarization basis set. Parallel theoretical studies were carried out for the valance isoelectronic S8 molecule, for which much experimental data exists. With double zeta plus polarization (DZ+P) self-consistent-field (SCF) theory vibrational frequencies and infrared and Raman intensities have been predicted. Cyclo-O8 is considerably more stable than experimental O–O bond energies would suggest and is predicted to lie only 94 kcal/mol above four infinitely separated O2 molecules.

Theoretical studies of oxygen rings: Cyclotetraoxygen, O4

An analogy is constructed between the known composition of elemental sulfur (principally S8 rings) and the unknown oxygen rings. Due to the weakness of O–O single bonds, as in hydrogen peroxide, it is hypothesized that oxygen rings are potential high energy density materials. A particularly attractive candidate is the O4 molecule, for which ring strain is expected to provide further destabilization relative to two separated O2 molecules. To pursue these qualitative suggestions, ab initio molecular quantum mechanics has been employed. Both self-consistent field (SCF) and configuration interaction including single and double excitations (CISD) methods have been employed in conjunction with double zeta plus polarization basis sets. At the highest level of theory the nonplanar (D2d point group, O–O–O–O torsional angle 25°) equilibrium structure is predicted to lie 2.9 kcal below the planar D4h structure, which is a transition state. The infrared spectrum is predicted at the DZ+P CISD level, as well as lower levels of theory. The O4 minimum is predicted to lie ∼100 kcal/mol above the asymptotic limit of two O2 molecules.