The Forbidden RotationalQ-Branch of CH3CF3: Torsional Properties and (A1−A2) Splittings

The pure rotational spectrum driven by the small distortion dipole moment perpendicular to the symmetry axis has been investigated between 8 and 18 GHz for CH₃CF₃in the ground vibrational state using a pulsed Fourier transform waveguide spectrometer. This molecule has been selected as a prototype for the case of a symmetric top with small (∼500 kHz) torsional energy splittings in the ground torsional state (ν₆= 0). In this state, six (k± 3 ←k)Q-branch series have been measured for lower stateK= |k| between 3 and 8 with 27 ≤J≤ 75. For (ν₆= 1), three series with lower stateKbetween 5 and 7 with 49 ≤J≤ 66 have been observed. In two of these series, the torsional fine structure extending over ∼6.8 MHz has been fully resolved. The (A₁−A₂) splitting has been measured in the (ν₆= 0) series (K= 6 ← 3) for 37 ≤J≤ 74. The global data set of 443 frequencies included avoided-crossing molecular-beam splittings of Meerts and Ozier (1991.Chem. Phys.152, 241–259) and mm-waveR-branch measurements of Bocquetet al.(1994.J. Mol. Spectrosc.165, 494–499). In a weighted least-squares analysis, a good fit was obtained by varying 18 parameters in a Hamiltonian that represented both the torsional effects and the sextic splittings. Effective values have been determined for both rotational constants, eight torsional parameters including the barrier height, six diagonal centrifugal distortion constants, and two centrifugal distortion constants (? and ?_J) that characterize the (Δk= ±3) matrix elements. The difficulties are discussed that arise in defining a unique model for the torsional terms in the Hamiltonian when a high barrier symmetric top is investigated by distortion moment spectroscopy. The redundancies are investigated that exist in the quartic and sextic Hamiltonian for a near-spherical top such as CH₃CF₃.     

Measurement of the frequency modulation transfer function of a laser using a Mach–Zehnder interferometer

A technique is presented for determining the frequency modulation transfer function of a laser. The method is based on a Mach–Zehnder interferometer, with a significant difference in the optical path lengths of the two arms. A frequency-modulated laser beam incident on the interferometer produces a phase-modulated photocurrent signal with an effective modulation index that is related to the amplitude of the optical frequency modulation. Techniques for determining both the amplitude and the phase of the optical frequency modulation from the photocurrent signal are described.     

Use of digital terrain data for calculating fire rates of spread with the PREPLAN computer system

This study reports a new technique for predicting fire rates-of-spread with the PREPLAN computer system used by the NSW National Parks and Wildlife Service. Accurate data on slope and topographic geometry produced by new digital terrain modelling packages are used to generate slope vectors in four directions for the McArthur equations. Rates-of-spread predicted using these new techniques are compared to those predicted using an existing technique that requires a calibration constant to avoid a tendency to overestimate. Data from a real fire in Kosciusko National Park are used, and suggest that almost all need for the calibration constant can be accounted for. The results suggest a way to significantly improve the accuracy of fire behaviour predictions.     

Diffraction effects in low-energy electron emission

The origin of diffraction peaks in the energy distribution of intensity of low-energy (< 1000 eV) electron emission from crystals is discussed from the standpoint of the dynamical theory of diffraction. The emitted electrons are considered to originate at relatively incoherent point sources in the crystal. The two-beam approximation of dynamical theory is used. The theory accounts for the chief regularities of diffraction peaks: temperature-dependence of peak intensities like that for low-energy electron diffraction (LEED) peaks, correlation of peak energies with X-ray absorption fine structure, and correlation of peak energies with the energies of normal-incidence LEED peaks in specular reflection. It is shown that the conditions for diffraction peaks coincide with the conditions for emergence of Kikuchi lines. It is predicted that for energies just above those of diffraction peaks, such emergences should be observable in the angular distribution of emission as intensity minima for emission along low-index crystal axes. Theory of Kikuchi band profiles is developed in an Appendix.     

Introducing Intellectual Property in an Undergraduate Chemistry Curriculum

An exercise that introduces undergraduate chemistry majors to concepts associated with intellectual property is outlined. The assignment includes an introduction to the terminology associated with starting a company based on intellectual property and to nondisclosure agreements. After this, the students write a draft patent application. With over 150,000 United States patents issued annually, the role of intellectual property is prominent and becoming increasingly important in current corporations and in the formation of new businesses, as well as in government and academic settings.     

Purity assignment for peptide certified reference materials by combining qNMR and LC-MS/MS amino acid analysis results: application to angiotensin II

Analytical and Bioanalytical Chemistry - The purity value assignment of metrologically traceable peptide reference standards requires specialized primary methods. Conventionally, amino acid...     

Total synthesis of the epidermal growth factor inhibitor (-)-reveromycin B

The total synthesis of the epidermal growth factor inhibitor reveromycin B (2) in 25 linear steps from chiral methylene pyran 13 is described. The key steps involved an inverse electron demand hetero-Diels-Alder reaction between dienophile 13 and diene 12 to construct the 6,6-spiroketal 11 which upon oxidation with dimethyldioxirane and acid catalyzed rearrangement gave the 5,6-spiroketal aldehyde 9. Lithium acetylide addition followed by oxidation/reduction and protective group manipulation provided the reveromycin B spiroketal core 8 which was converted into the reveromycin A (1) derivative 6 in order to confirm the stereochemistry of the spiroketal segment. Introduction of the C1-C10 side chain began with sequential Wittig reactions to form the C8-C9 and C7-C6 bonds, and a tin mediated asymmetric aldol reaction installed the C4 and C5 stereocenters. The final key steps to the target molecule 2 involved a Stille coupling to introduce the C21-C22 bond, succinoylation, selective deprotection, oxidation, and Wittig condensation to form the final C2-C3 bond. Deprotection was effected by TBAF in DMF to afford reveromycin B (2) in 72% yield.     

Species specific isotope dilution for the accurate and SI traceable determination of arsenobetaine and methylmercury in cuttlefish and prawn

Methods based on species specific isotope dilution were developed for the accurate and SI traceable determination of arsenobetaine (AsBet) and methylmercury (MeHg) in prawn and cuttlefish tissues by LC-MS/MS and SPME GC-ICPMS. Quantitation of AsBet and MeHg were achieved by using a ¹³C-enriched AsBet spike (NRC CRM CBET-1) and an enriched spike of Me¹⁹⁸Hg (NRC CRM EMMS-1), respectively, wherein analyte mass fractions in enriched spikes were determined by reverse isotope dilution using natural abundance AsBet and MeHg primary standards. Purity of these primary standards were characterized by quantitative ¹H-NMR with the use of NIST SRM 350b benzoic acid as a primary calibrator, ensuring the final measurement results traceable to SI. Validation of employed methods of ID LC-MS/MS and ID SPME GC-ICPMS was demonstrated by analysis of several biological CRMs (DORM-4, TORT-3, DOLT-5, BCR-627 and BCR-463) with satisfying results.     

Surface-state parameters from very low energy electron reflection data

A parametric form of the amplitude of elastic reflection of very low energy electrons is derived. The amplitude expression conforms to the results of an earlier analysis of a simple case of electron reflection called the quasi two-beam case. The parameters in the amplitude expression refer to: (1) the surface states of the crystal; (2) the band structure of the substrate crystal; and (3) absorption (inelastic scattering) in the energy range of the experiment The amplitude expression also includes parameters relating to (4) the behavior of the amplitude at infinity and at negative energy.The amplitude expression is used to parameterize existing experimental results for nickel (001) and for the surface formed by adsorption of sodium on nickel (001) to form the centered (2 × 2) structure. The parameterization employs previously-computed values of parameters relating to the nickel band structure [category (2) above], and parameters in categories (1), (3) and (4) are adjusted to fit the electron-reflection data. In the case of the sodium-covered surface it is shown that the shape of the intensity-energy curve and the general level of intensity relative to that for clean nickel depends critically on the surface-state parameters. Two surface states are needed to fit the intensity data The values of the surface-state parameters are: location relative to vacuum level: 2.5 ± 0.1, 6.9 ± 0.2eV; width: 4.2 ± 0.4, 7.5 ± 1.0eV. The classification and significance of surface-state resonances is discussed briefly.