Detection of the Elusive Triazane Molecule (N3H5) in the Gas Phase

We report the detection of triazane (N₃H₅) in the gas phase. Triazane is a higher order nitrogen hydride of ammonia (NH₃) and hydrazine (N₂H₄) of fundamental importance for the understanding of the stability of single‐bonded chains of nitrogen atoms and a potential key intermediate in hydrogen–nitrogen chemistry. The experimental results along with electronic‐structure calculations reveal that triazane presents a stable molecule with a nitrogen–nitrogen bond length that is a few picometers shorter than that of hydrazine and has a lifetime exceeding 6±2 μs at a sublimation temperature of 170 K. Triazane was synthesized through irradiation of ammonia ice with energetic electrons and was detected in the gas phase upon sublimation of the ice through soft vacuum ultraviolet (VUV) photoionization coupled with a reflectron‐time‐of‐flight mass spectrometer. Isotopic substitution experiments exploiting [D₃]‐ammonia ice confirmed the identification through the detection of its fully deuterated counterpart [D₅]‐triazane (N₃D₅).     

NMR observations of fluorine ion-implanted into polyacetylene and graphite

¹⁹FNMR spectroscopy has been used to characterize fluorine implanted into polyacetylene and highly orientated pyrolytic graphite. The intensities of the ¹⁹F NMR spectra at 4.5 K show that essentially all the fluorine is retained in these materials after the implantation process is over. The Une width of the spectrum of the graphite sample indicates that the fluorine remains where it was deposited.For the polyacetylene sample the ratio of the NMR solid echo height to the spin echo height, as calibrated herein, shows that the predominant nuclear diploar interaction of the implanted fluorine is heteronuclear.     

Describing and Evaluating an Exemplary Mathematics Elementary Staff Development Project

The purpose of this paper is to describe the model of a mathematics and science staff development cooperative and focus on the evaluation of the mathematics component. The Mathematics and Science Education Cooperative (MSEC) was a comprehensive, long‐range staff development program to improve the teaching and learning of mathematics and science at the elementary school level. The special features of MSEC were (a) it provided year‐round, multiyear involvement, and (b) each year an affective strand was included. Statistically significant student mathematics results from the years 1998–2000 are presented.     

Calculation of nuclear structure of205Pb relevant for the205Tl bdsolar neutrino detector

Energy spectrum and electromagnetic properties of²⁰⁵Pb have been studied in the cluster-vibration model (CVM). The lifetime of 0.3 ms was predicted for the 2.3 keV level which is of significance for considerations of the²⁰⁵Tl solar neutrino detector.     

Observation of symmetry lowering and electron localization in the doublet-states of a spin-frustrated equilateral triangular lattice: Cu3(O2C16H23) x 1.2C6H12

Cu3(O2C16H23)6.1.2C6H12, containing a Cu36+ core in an equilateral triangle geometry, has been found to be a versatile model system for investigating the spin-frustration phenomenon in a triangular lattice. It affords well-resolved EPR spectra from both of the two possible (Stotal = 1/2 and 3/2) spin states of the Cu36+ core. From 295 to 100 K, the spectra consist of a triplet, but with the central line overlapped by an additional, sharp peak, which replaces the triplet at 30 K and below. The triplet was thus assigned to the excited state with Stotal = 3/2, located at 324 +/- 5 K ( approximately 225 cm-1), with the zero-field parameters D = -535 G, E = 0, g parallel = 2.209 and g perpendicular = 2.057. The singlet was attributed to the Stotal = 1/2 state, with gxx = 2.005, gyy = 2.050, gzz = 2.282, and, surprisingly, a hyperfine splitting arising from a single Cu2+ nucleus, with Azz = 157 G. The detailed magnetic measurements on a three-electron, equilateral triangular system, and the observation of symmetry lowering in the doublet ground state, should be of broad theoretical and experimental interest in molecular magnetism.     

Characterizing NF and RO membrane surface heterogeneity using chemical force microscopy

Chemical force microscopy (CFM) was used to characterize the chemical heterogeneity of two commercially available nanofiltration and reverse osmosis membranes. CFM probes were modified with three different terminal functionalities: methyl (CH₃), carboxyl (COOH), and hydroxyl (OH). Chemically distinct information about the membrane surfaces was deduced based on differences in adhesion between the CFM probes and the membrane surfaces using both traditional atomic force microscopy (AFM) force measurements and spatially resolved friction images. Contact angle titration and streaming potential measurements provided general information about surface chemistry and potential, which largely complemented the CFM analyses, but could not match the accuracy of CFM on the atomic level. Using CFM it was found that both membranes were characterized as chemically heterogeneous. Specifically, membrane chemical heterogeneity became more significant as the scan size approached colloidal or micron-sized dimensions. In many instances, the chemically unique regions, contributing to the overall chemical heterogeneity of the membrane surface, were substantially different in chemistry (e.g., hydrophobicity) from that determined for the surface at large from contact angel and streaming potential analyses. Topographical and corresponding CFM images supports previous adhesion studies finding a correlation between surface roughness and the magnitude of adhesion measured with AFM. However, chemical specificity was also significant and in turn measurable with CFM. The implication of these findings for future membrane development is discussed.     

A vacuum ultraviolet laser photoionization and pulsed field ionization study of nascent S(3P2,1,0) and S(1D2) formed in the 193.3 nm photodissociation of CS2

The photoionization efficiency (PIE) and pulsed field ionization-photoion (PFI-PI) spectra for sulfur atoms S(3P2,1,0) and S(1D2) resulting from the 193.3 nm photodissociation of CS2 have been measured using tunable vacuum ultraviolet (vuv) laser radiation in the frequency range of 82 750-83 570 cm(-1). The PIE spectrum of S(3P2,1,0) near their ionization threshold exhibits steplike structures. On the basis of the velocity-mapped ion-imaging measurements, four strong autoionizing peaks observed in the PIE measurement in this frequency range have been identified to originate from vuv excitation of S(1D2). The PFI-PI measurement reveals over 120 previously unidentified new Rydberg lines. They have been assigned as Rydberg states [3p3(4S composite function nd3 D composite function (n=17-64)] converging to the ground ionic state S+(4S composite function) formed by vuv excitations of S(3P2,1,0). The converging limits of these Rydberg series have provided more accurate values, 82 985.43+/-0.05, 83 162.94+/-0.05, and 83 559.04+/-0.05 cm(-1) for the respective ionization energies of S(3P0), S(3P1), and S(3P2) to form S+(4S composite function). The relative intensities of the PFI-PI bands for S(3P0), S(3P1), and S(3P2) have been used to determine the branching ratios for these fine structure states, S(3P0):S(3P1):S(3P2)=1.00:1.54:3.55, produced by photodissociation of CS2 at 193.3 nm.     

A photodissociation study of CH2BrCl in the A-band using the time-sliced ion velocity imaging method

Employing a high-resolution (velocity resolution deltanu/nu<1.5%) time-sliced ion velocity imaging apparatus, we have examined the photodissociation of CH2BrCl in the photon energy range of 448.6-618.5 kJ/mol (193.3-266.6 nm). Precise translational and angular distributions for the dominant Br(2P32) and Br(2P12) channels have been determined from the ion images observed for Br(2P32) and Br(2P12). In confirmation with the previous studies, the kinetic-energy distributions for the Br(2P12) channel are found to fit well with one Gaussian function, whereas the kinetic- energy distributions for the Br(2P32) channel exhibit bimodal structures and can be decomposed into a slow and a fast Gaussian component. The observed kinetic-energy distributions are consistent with the conclusion that the formation of the Br(2P32) and Br(2P12) channels takes place on a repulsive potential-energy surface, resulting in a significant fraction (0.40-0.47) of available energy to appear as translational energy for the photo fragments. On the basis of the detailed kinetic-energy distributions and anisotropy parameters obtained in the present study, together with the specific features and relative absorption cross sections of the excited 2A', 1A", 3A', 4A', and 2A" states estimated in previous studies, we have rationalized the dissociation pathways of CH2BrCl in the A-band, leading to the formation of the Br(2P32) and Br(2P12) channels. The analysis of the ion images observed at 235 nm for Cl(2P(32,12)) provides strong evidence that the formation of Cl mainly arises from the secondary photodissociation process CH2Cl + hnu --> CH2 + Cl.