Rotationally resolved infrared absorption spectrum of N+4

Hydrogen Bond and π-π Stacking Interaction: Stabilization Mechanism of Two Metal Cyclo-N5 --Containing Energetic Materials

In recent years, cyclo-N₅ ^- has attracted extensive attention because all-nitrogen high-energy-density materials (HEDMs) have been expected to reach a TNT equivalent of over 3.0. However, for cyclo-N₅ ^--containing HEDMs, the stabilization mechanism has remained enigmatic. In this study, two typical cyclo-N₅ ^--containing metal hydrates, [Na(H₂O)(N₅)]·2H₂O (Na-cyclo-N₅ ^-) and [Mg(H₂O)₆(N₅)₂]·4H₂O (Mg-cyclo-N₅ ^-), are selected to gain insights into the factors affecting their stability by the first-principles method. Both binding/lattice energy calculations and density of states analysis show that Mg-cyclo-N₅ ^- is more stable than Na-cyclo-N₅ ^-. Hydrogen bonding is the main stabilization mechanism for stabilizing crystals and cyclo-N₅ ^-. Two types of hydrogen bonds, O-H···O and O-H···N, are clarified, which construct a 3D hydrogen bond network in Mg-cyclo-N₅ ^- and an intralayer 2D hydrogen bond network in Na-cyclo-N₅ ^-. Moreover, nonuniform stress causes distortion of cyclo-N₅ ^-. Comparing the two samples, the distortion degree of cyclo-N₅ ^- is higher in Na-cyclo-N₅ ^-, which indicates that cyclo-N₅ ^- decomposition is easier. These findings will enhance the future prospects for the design and synthesis of cyclo-N₅ ^--containing HEDMs.

High-resolution infrared spectroscopy of the charge-transfer complex [Ar–N2]+∙: A combined experimental/theoretical study

A combined experimental and theoretical study of the charge-transfer complex [Ar-N(2)](+) is presented. Nearly 50 transitions split by spin-rotation interaction have been observed by means of infrared diode laser absorption spectroscopy in a supersonic planar plasma expansion. The band origin is at 2272.2563(18) cm(-1) and rotational constants in the ground and vibrationally (NN-stretch) excited state amount to 0.128701(8) cm(-1) and 0.128203(8) cm(-1), respectively. The interpretation of the data in terms of a charge switch upon complexation is supported by new ab initio calculations. The best estimate for a linear equilibrium structure yields R(e)(NN)=1.102 A and R(e)(Ar-N)=2.190 A. Predictions for molecular parameters not directly available from the experimental results are presented as well. Furthermore, the electronic structure and Ar-N bonding mechanism of [Ar-N(2)](+) have been analyzed in detail. The Ar-N bond is a textbook example of a classical 2-center-3-electron bond.

Confirmation of the “long-lived” tetra-nitrogen (N4) molecule using neutralization-reionization mass spectrometry and ab initio calculations

Tetra-nitrogen (N(4)), which has been the subject of recent controversy [Cacace, d. Petris, and Troiani, Science 295, 480 (2002); Cacace, Chem. Eur. J. 8, 3839 (2002); Nguyen et al., J. Phys. Chem. A 107, 5452 (2003); Nguyen, Coord. Chem. Rev. 244, 93 (2003)] as well as of great theoretical interest, has been prepared from the N(4) (+) cation and then detected as a reionized gaseous metastable molecule with a lifetime exceeding 0.8 micros in experiments based on neutralization-reionization mass spectrometry. Moreover, we have used the nature of the charge-transfer reaction which occurs between a beam of fast N(4) (+) ions (8 keV translational energy) and various stationary gas targets to identify the vertical neutralization energy of the N(4) (+) ion. The measured value, 10.3+/-0.5, most closely matches that of the lowest energy azidonitrene (4)N(4) (+)C(s)((4)A(')) ion, resulting in the formation of the neutral bound azidonitrene (3)N(4)C(s)((3)A(")). Neutralization of the global minimum (2)N(4) (+)D( infinity h)((2)Sigma(u) (+)) ion leads to a structure 166 kJ mol(-1) above the dissociation products [N(2)((1)Sigma(g) (+))+N(2)((1)Sigma(g) (+))]; moreover, it was not possible to find a minimum on the (1)N(4) neutral potential energy surface for a covalently bonded structure. Ab initio calculations at the G3, QCISD/6-31G(d), and MP2/AUG-cc-pVTZ levels of theory have been used to determine geometries and both vertical neutralization energies of ions (doublet and quartet) and ionization energies of neutrals (singlet and triplet). In addition, we have also described in detail the EI ion source for the Ottawa VG ZAB mass spectrometer [Holmes and Mayer, J. Phys. Chem. A 99, 1366 (1995)] which was modified for high-pressure use, i.e., for the production of dimer and higher number cluster ions.

Coherent control in the presence of intrinsic decoherence: proton transfer in large molecular systems

An efficient semiclassical approach is developed and used to calculate the coherent-control map and time dependent decoherence measure for the excited-state proton transfer dynamics associated with the keto-enolic tautomerization reaction of 2-(2'-hydroxyphenyl)-oxazole. The method extends the usual bichromatic coherent-control scenario to simulate control at finite times after photoexcitation of the system. Extensive coherent control is demonstrated in a large molecule despite the ultrafast decoherence phenomena, providing results of broad theoretical and experimental interest.

Rotationally resolved infrared spectrum of the charge transfer complex [Ar-N2]+

Difficulties in preparing cluster ions for spectroscopic studies have limited our understanding of intermolecular forces in charged complexes that are typical of many reactive intermediates. Here, the infrared spectrum of the charge transfer complex [Ar-N2]+, recorded in a supersonic planar plasma with a tunable diode laser spectrometer, is presented. More than 70 adjacent rovibrational transitions were measured near 2272 wave numbers and assigned to the molecular nitrogen stretching fundamental in the 2Sigma+ ground state of [Ar-N2]+. The accurate structural parameters that were determined confirm a linear structure and show that the major part of the charge is located at the argon atom. The latter result is surprising and implies a charge switch of the cationic center upon complexation.

Experimental detection of tetranitrogen

Tetranitrogen (N4), which has been the subject of great theoretical interest, has been prepared from the N4+ cation and positively detected as a gaseous metastable molecule with a lifetime exceeding 1 microsecond in experiments based on neutralization-reionization mass spectrometry. An examination of the geometry of N4+ and the fragmentation pattern of the (14)N2(15)N2 neutral molecule has revealed that the latter is characterized by an open-chain geometry with two distinct, closely bound N2 units joined by a longer weaker bond.