Detection of autocatalytic decomposition behavior of energetic materials using APTAC

Characterization of autocatalytic decomposition reactions is important for the safe handling and storage of energetic materials. Isothermal differential scanning calorimetry (DSC) has been widely used to detect autocatalytic decomposition of energetic materials. However, isothermal DSC tests are time consuming and the choice of experimental temperature is crucial. This paper shows that an automatic pressure tracking calorimeter (APTAC) can be a reliable and efficient screening tool for the identification of autocatalytic decomposition behavior of energetic materials. Hydroxylamine nitrate (HAN) is an important member of the hydroxylamine family. High concentrations of HAN are used as liquid propellants, and low concentrations of HAN are used primarily in the nuclear industry for decontamination of equipment. Because of its instability and autocatalytic decomposition behavior, HAN has been involved in several incidents.     

High-Resolution Infrared Spectrum of the Ring-Puckering Band, nu(10), of Diborane

The spectrum of the nu(10) band of diborane, arising from the ring-puckering vibration, has been obtained with a spectral resolution of 0.0015 cm(-1) in the region 275-400 cm(-1). The spectrum of a sample enriched in (10)B was recorded as well as one with naturally abundant boron, i.e., 64% (11)B(2)H(6), 32% (10)B(11)BH(6), and 4% (10)B(2)H(6). This mode is the lowest vibrational level of the molecule and is unperturbed, allowing a complete assignment of not only the fundamental bands but also the 2nu(10)-nu(10) hot bands of all three boron isotopomers. The intensities of several hundred lines of the fundamental and hot bands of all isotopomers have been measured and vibrational transition moments have been obtained. Finally, it has been shown that the harmonic approximation does not apply for nu(10). Copyright 2000 Academic Press.     

Ultrafast magneto-optics in nickel: magnetism or optics?

Several magnetic and optical processes contribute to the magneto-optical response of nickel thin films after excitation by a femtosecond laser pulse. We achieved a first complete identification by explicitly measuring the time-resolved Kerr ellipticity and rotation, as well as its temperature and magnetic field dependence in epitaxially grown (111) and (001) oriented Cu/Ni/Cu wedges. The first hundreds of femtoseconds the response is dominated by state filling effects. The true demagnetization takes approximately 0.5-1 ps. At the longer (sub-ns) time scales the spins are found to precess in their anisotropy field. Simple and transparent models are introduced to substantiate our interpretation.     

The Pohlman cell as as a means of producing acoustic holograms

This paper reports the application of acoustic holography to a previously used non-destructive testing technique — the Pohlman Cell.     

On the barriers to planarity and the isotope effect in cyclobutane and cyclobutane-d8

The infrared and Raman data on the ring-puckering vibration in cyclobutane and cyclobutane-d₈ have been reexamined including the coordinate dependence of the reduced mass in the Hamiltonian. This was done for the purpose of estimating the importance of these small terms in the determination of barrier heights for four-membered rings and also on the determination of the dihedral angle corresponding to the potential minimum.The conclusions reached are that there is an isotopic dependence of the barriers to planarity in cyclobutane and cyclobutane-d₈ yielding a difference of ～14 cm^?1, but the precise value of the difference in barrier heights is ill determined. The higher-order kinetic energy terms in the Hamiltonian can account for a spread of ～3 cm^?1 in each of the barriers derived for cyclobutane and cyclobutane-d₈, depending on the details of the model used for the vibration, but not a difference of 14 cm^?1, which undoubtedly indicates the effects of coupling with other vibrational modes. It is also found that the derived values of the dihedral angles are quite sensitive to the details of the vibrational model, in fact, much more so than to the uncertainties in the bond distances and bond angles. A relationship between the potential constants derived for cyclobutane and cyclobutane-d₈ assuming an effective constant reduced mass and those derived for a semirigid model is demonstrated.