Assignment Of Lines Research Articles

CH 318OH: FIR laser line frequency measurements and assignments

Observations of far-infrared (FIR) laser emission and assignments of FIR laser lines have been reported in the literature for the O-18 isotopomer of methanol optically pumped by CO 2 lasers. So far, wavelengths have been measured for 100 FIR laser lines, and assignments for 26 of these lines have been proposed. However, some assignments were uncertain, with several possible alternatives, notably for the lines pumped by the 10R(20) CO 2 line. The present work combines new accurate FIR laser heterodyne frequency measurements with the results of Fourier transform spectroscopic studies of the CO-stretching and FIR torsion-rotation bands of CH 3 18 OH in a detailed analysis of the FIR laser emission. Precise frequencies have been determined for 22 of the laser lines, and five new laser lines have been observed. The spectroscopic results have led to unambiguous assignments for 20 of these lines and their confirmation through transition combination loops. The assignments of 13 of the lines are given for the first time. With the new results, the enigmatic 10R(20) situation has been almost completely resolved.

A Direct Method for the Analysis of AA′BB′ Spectra

Abstract A convenient new method for the direct analysis of well-resolved AA′BB′ spectra is presented. The repeated spacing structure is examined in detail to produce a new line assignment technique which forms the basis of the method. Conditions under which all the parameters may be determined are derived.

The D′ → A′ Transition in IBr: A Deperturbation Analysis

The D′2( 3 P 2) → A′2( 3Π) transition in IBr occurs with maximum intensity near 3850 Å when mixtures of I 2 and Br 2 in Ar are excited by a Tesla coil. Spectra are recorded photographically for I 79Br and I 81Br separately, and 24 v′- v″ bands spanning v′ = 0-5 and v″ = 11-17 are rotationally analyzed, yielding ∼3000 line assignments. Together with existing high-quality data covering the high- v′, low- v″ region, these data are analyzed through a deperturbation model which assumes that minor anomalies in the D′-state rotational constants are the result of weak interactions with the nearby β1( 3 P 2 state. This fit pins down the absolute energies of both states for the first time, yielding T e′ = 39 457(4) cm −1, T e″ = 11 437 (4) cm −1. Other primary spectroscopic constants (cm −1) are Δ T e = 28 019.22 ω′ e = 123.064, ω e x′ e = 0.2812, B′ e = 0.02860, ω″ e = 147.631, ω e x″ e = 1.260, B″ e = 0.04290, R′ e = 3.4806 Å, R″ e = 2.842 Å.

Assignments and Predictions of Optically Pumped Far-Infrared Laser Lines in [13C] Methanol and Associated High-Resolution Spectra

In this work, the high-resolution infrared (IR) spectrum of 13C-substituted methyl alcohol corresponding to the C-O stretch vibration and the far-infrared (FIR) spectrum corresponding to the torsional-rotational transitions have been recorded using a Fourier transform spectrometer. The results of detailed analyses of the spectra have been applied to propose new assignments of FIR laser lines pumped by the 9 P(34)CO2 laser line. These assignments involve highly perturbed levels in the first excited C-O stretch vibrational state. The assignments are supported by closed combination loops of accurately measured IR and FIR transitions. The analysis also yielded accurate frequencies for 17 potential FIR laser lines in [13C] methanol. The spectral data relevant to this work are presented. The FIR absorption spectroscopic study allowed us to evaluate the leading torsional-rotational molecular parameters for 13CH3OH in the vibrational ground state. The results of the high-resolution study will be useful for a precise model of the Hamiltonian for the excited C-O stretching state.

Planung der Kuppelproduktion in Systemen von chemischen Mehrzweckanlagen

AbstractPlanning of Coupled Production in Multipurpose Chemical Plant. This article considers strategies for computer‐aided planning of coupled production for systems of net worked multipurpose plant. Reasons are given for the failure of classical strategies such as are used in PPS systems. A procedure is described which, starting from a final product, automatically generates a cascade of previous product jobs and assigns them to production lines along a time axis (simultaneous material, pecursor, and production line assignment planning). Possibilities of interactive improvements of a given solution on consideration of factors such as storage costs and turnover are presented.

Beam-foil spectroscopy in the extreme UV of highly ionized silicon Si XI and the isoelectronic ions AI X, S XIII and Ar XV

Spectra of highly-ionized silicon, aluminium, sulfur and argon ions produced by the beam-foil technique have been analysed in the 5-40 nm wavelength range. Numerous transitions belonging to n = 3-4, 4-5 and 3-5 transitions arrays in the beryllium-like spectra Al X, Si XI, S XIII and Ar XV were observed for the first time. The assignment of spectral lines was corroborated by comparison along the isoelectronic sequence.

Assignments of methanol laser lines by frequency measurements and Fourier transform spectroscopy

We have measured the frequencies of four CH3OH far-infrared laser lines that were previously known only by wavelength measurement. Two of these lines turned out to be doublets, bringing the total number of measured lines to six. We can now confirm the assignments of five of them and definitely disprove the assignments proposed for the sixth. In particular we confirm the assignments for the four strong laser lines at 205 and 208 µm pumped by the 9-P(34) CO2 laser line. These lines share a common upper level in the first excited CO-stretch state, and terminate in the upper and lower levels of a hybrid state with J=5. Heterodyne frequency measurements and conventional microwave spectroscopy show that both lines are split into two components approximately 3.5 MHz apart. The origin of this further splitting is interpreted as a perturbed K-splitting.

On the interpretation and rotational assignment of degenerate four-wave mixing spectra: Four-photon line strengths for crossover resonances in NO A 2Σ+–X 2Π

We present here a set of equations specifically adapted to simulation of fully resonant, high-resolution, phase-conjugate degenerate four-wave mixing (DFWM) in molecular gases. Signal-intensity dependence on molecular wave functions, lifetimes, and laser beam polarizations is explicitly included in these equations. The emphasis of the presentation is on both physically intuitive interpretation and a practical, ‘‘cookbook’’ approach to spectral simulation. We present experimental verification of our calculations drawn from the spectrum of dilute NO in N2 at low pressures. Both degenerate two-level and three-level (crossover) resonances were observed. The experimental spectral intensities are accurately reproduced by the expressions presented here. We point out some of the subtleties of DFWM spectra that could be used as aids to interpretation, especially the use of laser polarization as a probe for spectral line assignments.

NQR and X-Ray Study of Bis(4-methylpyridinium) Pentabromoantimonate(III), (4-CH3C5H4NH)2SbBr5

Abstract The crystal structure of the title compound was determined (T = 300 K): , Z = 2, a = 1085.8, b = 1064.3, c = 929.0 pm, α = 97.83, β = 108.86, γ = 99.24°, R(F) = 0.047, Rw(F) = 0.041. Characteristic for the structure is the dimer structure of SbBr52− ion. The atomic coordination around the Sb atom is a distorted octahedron. The 81Br NQR spectrum was studied in the temperature range 77 ≤ T/K ≤ 350. The 81Br NQR frequencies are spread out over a wide range at 77 K: 37 ≤ ν(81Br)/MHz ≤ 111. The temperature dependence of the NQR frequencies and of their spread is given as is an assignment of 81Br NQR lines to the positions of Br atoms in the anion.

43Ca NMR Study of Bismuth-Based High-Tc Superconductors

Abstract As a first step of a study of the electronic properties of CuO2 planes by probing calcium nuclei in the bismuth-based high-Tc materials we report here the structural assignment of Ca NMR lines measured in 43Ca-enriched samples of n = 2 ((Bi,Pb)2Sr2CaCu2O8+x) and n = 3 ((Bi,Pb)2Sr2-Ca2Cu3O10+x) bismuth compounds. Powdered samples were investigated as well as oriented pow­ ders, achieved by uniaxial alignment of the grains in a 7T magnetic field. For the main calcium site (Ca between two CuO2 planes), we could determine the quadrupolar as well as the shift tensors. The results indicate that, in the same way as yttrium nuclei in YBaCuO, calcium nuclei are sensitive to the magnetic susceptibility of the metallic CuO2 planes.

New analysis for the assignment of UV-visible ionic Xe laser lines

Visible and UV laser emissions from a highly ionized pulsed Xe plasma were studied in relation to the ionic assignment of the laser lines. Time-resolved spectroscopy and intensity versus pressure analysis were used to determine the ionic origin of the studied lines. The results of both methods show good agreement, and the joint coincidence is used as a criterion for ionic classification, thus imposing a stringent condition for the assignment of the lines and enhancing its reliability. The disagreement between some of our assignments and those from other authors are discussed on the basis of the results of our systematic analysis of more than 200 spontaneous lines in the region of interest.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modern multidimensional protein NMR spectroscopy: I. Resonance assignment methods

Nuclear magnetic resonance spectroscopy (NMR) methods to study proteins have in the last five years moved from two-dimensional proton-only techniques to three-and four-dimensional triple- and quadruple-resonance techniques. The new methods allow more and more precise information to be extracted for the three-dimensional structure determination of the proteins in solution. This review focuses on these new techniques in relation to the assignment of NMR lines to the individual nuclei in the molecule.

Cardiotoxin III from the Taiwan Cobra ( Naja naja atra) : Determination of Structure in Solution and Comparison with Short Neurotoxins

The structure in solution of cardiotoxin III, a membrane toxin purified from the venom of the Taiwan cobra, Naja naja atra, is reported. Sequence-specific assignment of 1H-NMR lines was completed and the NMR data show the presence of a triple and a double-stranded antiparallel β -sheet. Many NOE cross peaks identified in NOESY spectra were applied as distance constraints based on a hybrid distance geometry/dynamical simulated annealing technique; 20 structures were found within a single family. The average value of atomic RMS differences between the 20 structures and their geometric mean is 0·087 nm for the backbone atoms and 0·152nm for all heavy atoms; they are 0·055nm and 0·12nm, respectively for the segments of secondary structure. In these selected structures the backbone of the polypeptide chain folds such that five strands emerge from a globular head. Three major loops link these strands to form a double and a triple-stranded antiparallel β-sheet. Comparison of the structures of the toxin in solution with the X-ray crystal structure of its homologous protein, cardiotoxin V II 4 from Naja mossambica mossambica, showed good agreement between the structures except at segments of the turns. As the functions of short neurotoxins and cardiotoxins are distinct, despite their similar secondary structural patterns and tertiary folding, a comparative analysis has been carried out between cardiotoxin III and short neurotoxins of known structures. We discuss their structural features in order to clarify relationships between their structure and function.

The laboratory spectrum of acetaldehyde at 1 millimeter (230-325 GHz)

The rotational spectrum of acetaldehyde (CH3CHO) in the frequency range 230-325 GHz has been measured in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Over 250 transition frequencies are presented for this molecule for both A and E symmetry species in its ground (upsilon<SUB>t</SUB> = 0) and first excited (upsilon<SUB>t</SUB> = 1) torsional state, with experimental uncertainties of +/- 50 kHz. The data were fitted with a model involving an internal rotation potential function, which typically reproduces the measured frequencies to nu<SUB>obs</SUB> - nu<SUB>calc</SUB> less than or approximately 50 kHz for both ground and upsilon<SUB>t</SUB> = 1 state. These newly measured rest frequencies should aid in the identification of interstellar CH3CHO and in spectral line assignments for millimeter-band scans.

Divide‐and‐conquer, pattern matching, and relaxation methods in interpretation of 2‐D NMR spectra of polypeptides

AbstractOne task in the interpretation of the 2‐D nuclear magnetic resonance (NMR) spectrum is to assign its signal patterns to their corresponding amino acids in proteins or polypeptides. To carry out this task of interpretation, one requires sufficient chemical knowledge and expertise to reason from a set of highly noisy data. We present a system called RUBIDIUM (a Rule‐Based Identification in 2‐D NMR Spectrum) to formulate the expertise and automate the process of interpretation. Given a protein or polypeptide with a known amino acid sequence and the 2‐D NMR spectra (both COSY and NOESY), RUBIDIUM yields plausible assignments of lines that account for most signals observed in the spectrum and conform to prior chemical knowledge. Rules of pattern matching are used to detect plausible signal patterns. The expertise of the sequence‐specific assignment task is formulated to assign a signal pattern to amino acids. To cope with ambiguities and noise, RUBIDIUM adopts various low‐level data preprocessing techniques, the strategy of divide and conquer, and the relaxation technique to decrease the complexity and recover from overconstrained conditions. The polypeptides oxytocin and vasopressin are used to illustrate the performance of RUBIDIUM. © John Wiley &amp; Sons, Inc.

Secondary Structure and Protein Folding of Recombinant Chloroplastic Thioredoxin Ch2 from the Green Alga Chlamydomonas reinhardtii as Determined by 1H NMR1

The recombinant form of the chloroplastic thioredoxin Ch2 from the green alga Chlamydomonas reinhardtii [Jacquot et al. (1992) Nucleic Acids Res. 20, 617] that preferentially activates the NADP dependent malate dehydrogenase [EC 1.1.1.82] (m-type thioredoxin) through a light promoted reductive system, has been subjected to an extensive two-dimensional 1H NMR analysis. A complete 1H NMR assignment of the resonance lines in both the oxidized and the reduced states at pH 5.8 has been obtained allowing the recognition of the secondary structure patterns and the global protein folding. The single polypeptide chain, made of 106 residues plus one additional Met located at the N-terminal position (11.6 kDa) due to the protein expression system, folds into a pattern characteristic of the open twisted alpha/beta structures already found for Escherichia coli and human thioredoxins for which the protein shares 46 and 20% of sequence identity, respectively. The open alpha/beta structure is made of 5 beta-sheets associated in a parallel (beta 1 to beta 3) and anti parallel manner (beta 3 to beta 5) and surrounded by 4 helices. This represents the first structural exploratory study of the ubiquitous oxido-reductase thioredoxins in a photosynthetic living system.

Application of f1-Decoupled 2D-NMR Methods for Characterizing the Stereochemical Structure of tert-Butyl Acrylate Oligomers

The stereochemical structure of tert-butyl acrylate (tBuA) oligomers prepared in tetrahydrofuran with tert-butyl-α-lithioisobutyrate initiation was studied by NMR methods. By combination of various types of one- and two-dimensional NMR methods, resonance lines could be assigned in 1H and 13C NMR spectra of tBuA oligomers (dimer, trimer, tetramer and pentamer) in C6D6 solution. The unequivocal assignment of NMR resonance lines to various stereoisomers in the tBuA tetramer and pentamer was achieved by means of the f1-decoupled COSY experiment. The two isomers present in the sample of tBuA tetramer could be identified as m (major form) and r (minor form) by means of the f1-decoupled NOESY experiment; their populations amounted to 0.78 and 0.22, respectively. In the sample of tBuA pentamer, the populations of the stereoisomers were mm:mr:rm=0.635:0.185:0.180; the population of the rr stereoisomer is negligible (does not exceed 0.05). These stereoisomer populations in the tBuA pentamer conform to Bernoullian statistics.

Solid-state NMR investigation of the novel microporous gallophosphate cloverite

The investigation of the gallophosphate molecular sieve cloverite by solid-state 13C, 31P, and 71Ga NMR techniques is described. Comparison of the 13C CP/MAS spectra of cloverite quinuclidine and quinuclidinium chloride give further evidence that the templating amine is protonated. The non-spinning CP experiment shows the full chemical shift anisotropy and reveals no motion of the template molecules. The 1H-decoupled 31P MAS spectrum of cloverite exhibits very poor resolution. However, the resonance lines of the five crystallographically independent 31P atoms are resolved by applying a dipolar-dephasing technique which utilizes differences in dipolar 31P—1H interactions. CP/MAS experiments with variable contact times and a depolarization experiment support this result and allow partial assignment of resonance lines to two groups of 31P atoms. The experimental conditions for 71Ga CP/MAS experiments were evaluated using Ga2(SO4)3·18H2O as a model substance. Application to cloverite with decreasing contact times shifts the maximum of the main signal from − 41 to − 26 ppm, thus indicating the presence of gallium sites with different cross-polarization dynamics.

Charge-transfer transitions and pseudoacceptor states of iron in gallium phosphide.

We report transient shallow bound-hole states of the deep ${\mathrm{Fe}}^{3+/2+}$ acceptor level of iron in GaP, which appear close to the photoionization onsets at 0.82 and 1.23 eV. Optical-absorption spectra with improved signal-to-noise ratio and results from photoluminescence excitation show additional lines not reported hitherto. These data require an assignment of absorption lines which were reported recently. As already outlined for InP and GaAs, we discuss all lines as charge-transfer transitions, a model which is based on transient shallow bound-hole states of a pseudoacceptor. We compare the ground state of the shallow bound hole with the ${\mathrm{Fe}}^{2+}$-related deep acceptor in the three semiconductors InP, GaAs, and GaP. The transient shallow acceptor ground state is bound by about 1/20 of the ionization energy of the corresponding deep acceptor state.

Laser mechanisms and processes in the p-GE far IR laser

Laser mechanisms in the p-Ge far IR laser are identified and models presented to make laser line assignments in the three laser spectral regions: (A) multiple frequencies non-tunable with E and B, (B) multiple frequencies tunable with B, and (CR) single cyclotron frequencies tunable with B. Brief reviews of the classical and quantum theories of the p-Ge laser are given to support and explain the laser models.