Interfering proton and neutron transfer in the reaction C(N, N)C

Elastic scattering and one-nucleon transfer reactions induced by ¹⁶O have been investigated in the energy region 45–60 MeV on targets of ²⁶Mg, ²⁷Al, ³⁰Si and ⁴⁸Ca. Angular distributions were measured in the angular range 4°–40°. Optical model parameters were derived from the elastic scattering data and the transfer reaction data were analysed using both no-recoil and full-recoil DWBA codes. In the case of proton transfer reactions on ⁴⁸Ca, good agreement was obtained between the data and the DWBA calculations while the data for the lighter targets could not be satisfactorily reproduced. The oscillatory pattern of the angular distributions is discussed in terms of the three-parameter model of Kahana, and it is found that the model qualitatively explains the observed transition from smooth to oscillatory angular distributions.     

Exceptional points in atomic spectra

We report the existence of exceptional points for the hydrogen atom in crossed magnetic and electric fields in numerical calculations. The resonances of the system are investigated and it is shown how exceptional points can be found by exploiting characteristic properties of the degeneracies, which are branch point singularities. A possibility for the observation of exceptional points in an experiment with atoms is proposed.     

Infrared Spectrum of Pyromellitic Diimide HN(CO)2C6H2(CO)2NH

The IR spectrum of pyromellitic diimide, HN(CO)₂C₆H₂(CO)₂NH, has been measured for polycrystalline sample. The observed bands have been assigned to the IR active fundamentals and combinations on the basis of a D_2h molecular symmetry by comparison with those of pyromellitic dianhydride. Band shifts from dianhydride to diimide were observed for the 0[dbnd]C-X-C[dbnd]O fundamentals and the N-H modes have been assigned by comparison with those reported for phthalimides.     

Vacuum mass spectra for SU(N) self-dual Chern-Simons-Higgs systems

We study the SU(N) self-dual Chem-Simons-Higgs systems with adjoint matter coupling, and show that the sixth-order self-dual potential has p(N) gauge inequivalent degenerate minima, where p(N) is the number of partitions of N. We compute the masses of the gauge and scalar excitations in these different vacua, revealing an intricate mass structure which reflects the self-dual nature of the model.     

Improved resolution in (13)C solid-state spectra through spin-state-selection

The application of a spin-state-selective coherence transfer experiment (INADEQUATE-SSS) to solid-state NMR spectroscopy is described. Two-dimensional (13)C double-quantum/single-quantum spectra without J splittings in both dimensions lead to enhanced spectral resolution. The method is demonstrated to significantly improve the spectral resolution of the crowded C'-C(alpha) region of two proteins.     

Clusters and magnetic anchoring points in (Ga,Fe)N condensed magnetic semiconductors

The stability and magnetic properties of Fe clusters in the (Ga,Fe)N magnetic semiconductor is investigated by using first-principles density functional theory and local spin density+Hubbard U theoretical methods. The present results reveal the existence of ferrimagnetic clusters formed by three or four peripheral Fe atoms neighboring a central Fe atom acting as a robust magnetic anchoring point. These clusters have magnetic moments 2 or 3 times that of a single Fe atom and, when connected by sharing peripheral Fe atoms, can form stable, ordered magnetic regions where all of the central atoms are ferromagnetically coupled. The formation of these ferrimagnetic clusters is proposed here to be at the origin of the ferromagnetic behavior observed in (Ga,Fe)N samples showing chemical phase separation.     

N(2)-Broadening Coefficients in the nu(1) Band of (35)Cl(12)C(14)N

N(2)-broadening coefficients have been measured for 30 lines of cyanogen chloride ((35)Cl(12)C(14)N) at room temperature in the P and R branches of the nu(1) band, using a tunable diode-laser spectrometer. These lines, with J values ranging from 0 to 55, are located in the spectral range 694-736 cm(-1). The collisional widths are obtained by fitting the spectral lines with a Voigt and a Rautian profile. The broadenings coefficients of (35)ClCN-N(2) have also been calculated from a semiclassical theory involving the atom-atom Lennard-Jones model for the intermolecular potential in addition to electrostatic interaction. Copyright 2000 Academic Press.     

Three-dimensional protein NMR TROSY-type (15)N-resolved (1)H(N)-(1)H(N) NOESY spectra with diagonal peak suppression

An earlier two-dimensional NOESY experiment with diagonal peak suppression in the (1)H(N)-(1)H(N) region is extended to three dimensions by including (15)N evolution while maintaining the TROSY approach throughout. The technique suppresses all anti-TROSY resonances by appropriate pulse sequence elements and for large molecules at high fields possible semi- and anti-TROSY artifacts are further suppressed by virtue of much shorter transverse relaxation times for these components. The new technique is demonstrated using an (15)N-labeled protein sample, RAP 17-97 (N-terminal domain of alpha2-macroglobulin Receptor Associated Protein), in H(2)O at 500 MHz.     

Photoluminescence spectra of laser-synthesized Si/C/N ultrafine powders

Ultrafine Si/C/N ceramic powders were synthesized by a CO₂-laser-induced reaction between silane (SiH₄), ammonia (NH₃) and acetylene (C₂H₂). The powders were characterized by infrared (IR) reflection and photoluminescence (PL) spectroscopy. From the infrared reflection spectra of Si/C/N powders, we have identified the causes of the strong photoluminescence present in these powders. The photoluminescence spectra of Si/C/N powders originate from the presence of hydroxylated and amorphous silicon (a-SiO₂) formed at the porous surface of these powders. We have shown that different chemical bonding between Si, C and N atoms, the degree of crystallinity of ternary powders and their porosity strongly influence the processes at their surface, i.e. the formation of amorphous silicon and silanole. Received: 16 June 2000 / Accepted: 24 June 2000 / Published online: 9 November 2000     

Tailorable acceptor C(60-n)B(n) and donor C(60-m)N(m) pairs for molecular electronics

Our first-principles calculations demonstrate that C(60-n)B(n) and C(60-m)N(m) can be engineered as the acceptors and donors, respectively, needed for molecular electronics by properly controlling the dopant number n and m in C60. We show that acceptor C48B12 and donor C48N12 are promising components for molecular rectifiers, carbon nanotube-based n-p-n (p-n-p) transistors, and p-n junctions.     

Rotational spectra of the 13C and 15N isotopic species of cyanoacetylene

Ground vibrational state rotational transitions have been measured in the frequency region 8 to 220 GHz for the following four isotopic species of cyanoacetylene: H¹³CCCN, HC¹³CCN, HCC¹³CN, and HCCC¹⁵N. The improved rotational constants were used for accurate frequency predictions for any transition not measured in this frequency range. Cyanoacetylene was produced efficiently by a radiofrequency discharge in a mixture of HCCH and HCN; this technique provides a convenient method for specific isotopic enrichment of this molecule.     

Complex probabilities on R(N) as real probabilities on C(N) and an application to path integrals

We establish a necessary and sufficient condition for averages over complex-valued weight functions on R(N) to be represented as statistical averages over real, non-negative probability weights on C(N). Using this result, we show that many path integrals for time-ordered expectation values of bosonic degrees of freedom in real-valued time can be expressed as statistical averages over ensembles of paths with complex-valued coordinates, and then speculate on possible consequences of this result for the relation between quantum and classical mechanics.     

Determination of internucleotide (h)J(HN) couplings by the modified 2D J(NN)-correlated [(15)N, (1)H] TROSY

Recent developments in the direct observation of J couplings across hydrogen bonds in proteins and nucleic acids provide additional information for structure and function studies of these molecules by NMR spectroscopy. A J(NN)-correlated [(15)N, (1)H] TROSY experiment proposed by Pervushin et al. (Proc. Natl. Acad. Sci. USA 95, 14147-14151, 1998) can be applied to measure (h)J(HN) in smaller nucleic acids in an E.COSY manner. However, it cannot be effectively applied to large nucleic acids, such as tRNA(Trp), since one of the peaks corresponding to a fast relaxing component will be too weak to be observed in the spectra of large molecules. In this Communication, we proposed a modified J(NN)-correlated [(15)N, (1)H] TROSY experiment which enables direct measurement of (h)J(HN) in large nucleic acids.     

(C_5H_(11)N_2)~+和(C_7H_(12)N_2)~(2+)的NMR研究

结合1H NMR,13C NMR谱,分别对钨、钼配合物{WO2(C10H6O2)2(C5H11N2)2[H2N(CH2)3NH2]}3(1),{(C5H11N2)2[H2N(CH2)3NH2][MoO2(C10H6O2)2]}(2),{(C7H12N2)2[MoO2(C10H8O2)2]}(3)晶体结构中小分子环进行了归属.其中,配合物1和2中(C5H11N2)+的NMR研究证实了六元环由1,3-丙二胺和乙腈化合而成,配合物3中(C7H12N2)2+的NMR谱图证实了七元环由乙二胺和乙酰丙酮化合而成,并且推导出这些亲核加成-消除反应的反应机理.配合物1~3中的小分子环的合成在其它体系中尚未见报导,而在合成它们的反应中作为新产物随主体晶体析出,并由晶体结构解析和NMR得到了证实.     

The Optical Properties of (C59N)2

Using the extended Hubbard model and sum-over-state method, we have calculated the linear polarizability α and the third-order nonlinear polarizability γ for (C₅₉N)₂. We find that (C₅₉N)₂ has very big γ value (around esu), and its α and γ values are bigger than those of C₅₉N. In particular, when 1.2 eV≤3ω, (C₅₉N)₂ as much larger γ values than C₅₉N.