Ammonium perchlorate structure and dynamics at low temperatures

Comparative DFT and DFT-D studies on structural, electronic, vibrational and absorption properties of crystalline ammonium perchlorate

Pressure-induced rearrangement of the relative position of anions and cations in AP crystal.

Temperature dependence of thermal expansion tensors of energetic materials

Unit-cell values as well as thermal expansion tensors for 13 energetic materials are calculated from variable-temperature X-ray diffraction data. The thermal expansion tensors and their temperature dependence are reported numerically, algebraically and graphically.

THEORETICALLY EXPLORING METHYLATION EFFECTS ON SOLVATED MULTI-HYDROGEN BONDING AMMONIUM PERCHLORATE SYSTEMS

Methyl substituents are introduced into solvated ammonium perchlorate (AP) systems to explicate the effects of methylation on localized hydrogen-bonding. Methylation systems are modeled using density functional theory (DFT) B3LYP type with 4-31G(d, p), 6-311+(2d, p) basis set methods, indicating that whichever methyl group is substituted at the proton site in an ammonium ion or solvent, both methyl groups cease to H-bond, as evidence by elongation of the neighboring bond and characteristic red-shifts in the frequency of vibration. The energy barriers to the conversion from reactants to products in solvated AP systems are also discussed herein to help to elucidate the relationship solubility and H-bonding.

Anisotropy of the proton T1 and the low-field relaxation in NH4 ClO4 below 20K

The spin-lattice relaxation of protons in NH4ClO4 at low temperatures has been studied theoretically and experimentally. The NH4 librational tunneling determines the spin-librational wavefunctions, which are derived first. The dominant transition rates related to the magnetic dipolar interaction between the NH4 protons are then obtained. They reproduce well the angular dependence of the proton relaxation time. When all the transition rates are taken into account, both the temperature and frequency dependence of the relaxation rate agree with our experimental data for a powder sample. Reasons for the non-exponential relaxation are discussed. Apart from the angular dependence of the relaxation rate, they include the tunnel frequency distribution, the coupling to the tunnel reservoir and the effect of deuterons in their natural concentration.

Deuteron NMR spectra of ND4ClO4 single crystal at low temperatures

2H NMR spectra of ND4ClO4 single crystal were obtained at v0 = 44 MHz. Orientation and temperature (1.9-75 K) dependences were measured. Fitting the spectra gives the effective quadrupole coupling constants for all deuterons and the ground torsional level structure. The isotope reduction of the (A-T) and (A-E) tunnelling splittings, i.e., the ratios of the respective splittings for NH4+ and ND4+, were found to be different. The splittings at T = 24 K are about 60% of the helium temperature values. The spectrum undergoes intermediate narrowing by reorientations between 26 and 34 K and tunnelling related features in the spectra are eradicated. After reaching the extreme narrowing limit, a doublet with gradually decreasing separation was observed, what was attributed to averaging by torsional oscillations of increasing amplitude. At high temperatures (T > 75 K), the narrow spectrum reflects fast multiaxial reorientation of the ammonium ion.