Energy transfer from Ca(3P) to Sr and quenching of Sr(3P) by the inert gases

A laser-induced fluorescence technique has been used to measure the rate of the energy-transfer reaction Ca(³P) + Sr(¹S) α Ca(¹S) + Sr(³P). Rates for quenching Sr(³P) by inert gases were also measured and correlated with an orbiting model.     

Singlet methylene kinetics: Direct measurements of removal rates of ã1A1 and b̃1B1 CH2 and CD2

Rate constants for collisional removal of ã¹A₁ and b?¹B₁ CH₂ and CD₂ have been directly measured, using IR laser induced multiple photon dissociation to prepare the radicals, and time resolved laser induced fluorescence to observe them. For CH₂(ã¹A₁) removal by He, Ne, Ar, Kr, Xe, N₂, H₂, O₂, CO and CH₄, rate constants of 3.1, 4.2, 6.0, 7.0, 16, 8.8, 130, 30, 56 and 73 × 10^?12 cm³ molecule^?1 s^?1 were found respectively. These represent significant increases over the previously accepted values. Essentially no isotope effect is observed in the removal of CD₂(ã¹A₁) by the rare gases. The rate determining step in removal by the rare gases and N₂ is thought to be singlet—triplet intersystem crossing controlled by long range attractive forces, and the results are discussed in terms of both isolated and mixed state theoretical models of these processes. For the other molecular collision partners, bimolecular chemical removal channels are possible, and may account for the relatively fast rates observed. Radiative lifetimes of five Σ vibronic levels of CH₂(b?¹B₁) and three Σ vibronic levels of CD₂(b?¹B₁) have been measured and found to lie in the range 2.5–6.0 μs, and collisional quenching rates for CH₂(b?¹B₁) are found to be of the order of the gas kinetic collisional frequency.     

Collision-induced dissociation of dye-laser excited Li2(A 1Σ+u)

Li₂ molecules in a vapour cell were excited into the A ¹Σ⁺_u state using a dye laser set at 6103 Å. In the presence of a foreign gas Li(2 ²P) atoms were detected by means of the Li(3 ²D-2 ²P) transition which was simultaneously excited by the 6103 Å radiation. From the pressure dependence of the normalized Li fluorescence intensity absolute rate constants for collision-induced dissociation Li₂(A) → Li(2 ²P) by the five rare gases were determined. The results are compared with recent work on the analogous process in the Li₂(B ¹Π_u) state and with other systems.     

Physical and chemical forms of radionuclides of 38S, 38Cl, 39Cl, and 82Br, produced at a high-energy proton accelerator facility

High-energy protons and neutrons produce various radionuclides in the air, mainly through the nuclear spallation of atmospheric elements. Air samples were collected from the EP-2 tunnel of the KEK 12 GeV proton synchrotron facility with a filter pack, which consisted of a membrane filter for aerosols, a Na₂CO₃-impregnated filter for acidic gases, and an activated carbon fiber filter for non-acidic gases. Sulfur-38 was found on the membrane and Na₂CO₃-impregnated filters, ³⁸Cl and ³⁹Cl were on the membrane, Na₂CO₃-impregnated, and ACF filters, and ⁸²Br was only on the ACF filter. The results on the relative abundances of aerosol and gaseous acidic components have indicated that ³⁸Cl produced by thermal neutron capture, which is the main reaction for ³⁸Cl production in the EP-2 tunnel air, are likely not to be present as aerosol or acidic gas. This was similar to the case of ⁸²Br produced by thermal neutron capture.     

Deactivation of vibrationally excited CD3H using laser-induced fluorescence

Infrared fluorescence observed after exciting to ν₆ (ν=1) of CD₃H with a Q-switched CO₂ laser yields the exponential deactivation rate constant of 0.84 ms^?1 torr^?1. Rate constants for deactivation of CD₃H by rare gases vary from 1.4 (for He) to 0.029 (for Xe) ms^?1 torr^?1.     

Reaction rate studies of atomic germanium (3P0,1) and silicon (3PJ) with various oxidizers

The gas phase reactions of Ge(³P_0,1) and Si(³P_J) with O₂, NO and N₂O have been studied in a flow tube system at 350 K. Atomic Ge and Si were produced by flowing GeH₄ and SiH₄ through a hollow cathode discharge. The subsequent disappearance of the Ge and Si atoms was followed with atomic absorption spectroscopy. Rate constants were determined for the reactions at 4 and 5 torr pressures.     

Velocity dependence of the penning ionization cross section of D atoms by He (2 1S) and He (2 3S) atoms

Measurements of the Penning ionization cross section, σ_PI of D atoms by metastable He atoms show that σ_PI for the reaction He (2 ¹S) + D is much larger than σ_PI for He (2 ³S) + D. In the relative velocity range ν_r = (2.3–4.8) × 10⁵ cm/s (0.037–0.163 eV), σ_PI for He (2 ¹S) + D collisions was found to vary as ν_r^?0.33.     

Energy-transfer reactions between He(2 3S) and Ne(3P0.2) metastable atoms and PN radicals

Energy-transfer reactions between He(2 ³S) and Ne(³P_0.2) metastable atoms and PN radicals have been investigated by emission spectroscopy. Thirteen new PN⁺ (B ¹Σ⁺ ?X ²Σ⁺) emission bands were found in addition to eight previously identified bands in the range 305–395 nm. From these observed band-head wavelengths, the following molecular constants were obtained for the X and B states of PN⁺ : PN⁺ (X): ω_c = 1306 ± 3 cm^?1, ω_cx_c = 7.9 ± 0.7 cm^?1, PN^? (B): T_c = 31354 ± 6 cm^?1, ω_c = 719 ± 3 cm^?1, ω_cx_c = 1.6 ± 0.7 cm^?1. The PN⁺ (B) state vibrational population was estimated from the emission intensities and the calculated Morse Franck—Condon (FC) factors for the PN⁺ (B–X) transition. Both the results obtained by He(2 ³S) and Ne(³P_0.2) Penning ionization shifted to lower vibrational levels in comparison with the calculated FC factors for vertical PN(X) → PN⁺ (B) ionization. Besides PN⁺ (B–X) emission, unidentified bands were observed in the 231–236 nm region in the helium afterglow, probably originating from PN or PN^?.     

Inductive substituent constants σji from olefinic geminal 1h, 1h nmr coupling constants

Theoretical and experimental arguments are presented supporting the postulate that olefinic NMR coupling constants ²J_HH are insensitive to β-substituent influences on the olefinic π orbital. A new set of substituent constants, σ^J_I, is proposed to measure directly the inductive substituent effect transmitted by σ-bonds. The previously available range of inductive substituent constants can be appreciably extended in this way. Comparisons of σ^J_I with other observables and parameters for selected substituents are made as a test of consistency.     

Deactivation of He 23S by thermal electrons

The rate coefficient for deactivation of the metastable 2³S state of He by impact of thermal electrons is deduced from recent calculations of inelastic electron-He cross sections. The deactivation rate is found to be nearly constant with temperature. Computed values range between 2.82 and 3.03 (10^?9 cm³/sec) for T between 0 and 2000°K. De-excitation cross sections are given for low-energy incident electrons.     

Reactions of 12C+ with hydrocarbons at 296 K:carbon-carbon bond formation

Rate constants and product distributions have been determined for the ion-molecule reactions between ¹²C⁺ and methane, ethane, propane, ethylene, propylene, allene, acetylene, propyne and benzene. The measurements were carried out with the SIFT technique at a temperature of 296 ± 2K. The results provide insight into the build-up of carbon skeletons to form C⁺_n+1 ions and other competing modes of reaction at room temperature.     

Laser-fluorescence measurement of the 7LiD (X 1∑+) potential up to high vibrational quantum numbers

Sixteen new vibrational levels of ⁷LiD (X ¹∑⁺) were found by analysis of laser-excited fluorescence spectra. They extend up to ν″ = 20, corresponding to 82% of the dissociation energy of LiD. New rotational and vibrational constants were derived from the data and were used for an RKR calculation of the ⁷LiD (X ¹∑⁺) potential. Extra-polating this potential up to the dissociation limit gives agreement with the known dissociation energy to within 90 cm^?1.     

Instrumentelle Kompensation des Quencheffektes bei der Bestimmung von 14C und 35S

Zusammenfassung Ein Quencheffekt tritt auch nach Oxydation der organischen Probe auf. Dieser ist bedingt durch gewisse Verbrennungsprodukte, wie NO₂, Halogene, SO₂ und SO₃. Es wurde gefunden, da\ man den Quencheffekt der Verbrennungsprodukte bei der Bestimmung von ¹⁴C und ³⁵S ausschalten kann, wenn man die Spannung des Data-Photomultipliers bis zu einem gewissen Punkt (Kompensationspunkt) erhöht und die Messung in einem ZÄhlfenster durchführt. Der Kompensationspunkt wird graphisch ermittelt; hierzu mi\t man die ZÄhlrate des reinen Absorbens sowie die ZÄhlrate des Absorbens, das die maximal zu erwartende Menge Verbrennungsprodukt enthÄlt, bei verschiedenen Data-Spannungen. Der Zusammenhang zwischen der instrumenteilen Kompensation und dem Energiespektrum von ¹⁴C wird aufgezeigt. Bei der Bestimmung von Tritium lÄ\t sich der Quencheffekt nicht kompensieren, denn das Energiespektrum von Tritium wird durch eine Quenchverbindung anders beeinflu\t als das Spektrum von ¹⁴C bzw. ³⁵S.

---

Summary After combustion of the organic sample a quenching effect is observed, due to several combustion products as NO₂, halogens, SO₂, and SO₃. We found, that it is possible to eliminate quenching of the combustion products in the determination of ¹⁴C and ³⁵S, if the high voltage of the data-photomultiplier is raised to a certain level (compensation point) and if the counting is performed in a window. The compensation point is calculated graphically by determining the counting rate of the pure absorbant and the absorbant plus the highest expected amount of combustion products. The relation between instrumental compensation and the energy spectrum of ¹⁴C is elucidated. It is not possible to compensate quenching in the determination of tritium, because the energy spectrum of ³H is influenced in a different way than the spectrum of ¹⁴C and ³⁵S.

     

Calculation of 1J(13C-29si) spin-spin coupling constants by the maximum overlap approximation method

The spin-spin ¹J(C-Si) coupling constants were calculated by the maximum overlap approximation method for a series of related organosilicon compounds. It was concluded that the variation in hybridization of the relevant carbon atom accounts for the changes in ¹J(C-Si) observed experimentally.     

Rotational analysis of the 201 and 211 bands in the Ã2Σ+-X̃ 2Π spectrum of N2O+

Analysis of new emission spectra of òΣ⁺-X? ²Π in N₂O⁺, including the forbidden components with Δν₂ = 1, have made it possible to locate all four vibronic components of the ν″₂ = 1 manifold. Principal rotational constants and spinvibronic terms are given. A previous estimate of the Renner parameter is revised to a value of ?0.179 ± 0.002.     

NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

Aufkl?rung der 1H- und 13C-NMR-spektren sowie der kristallstruktur unges?ttigter glycosylphosphonate und konformationsberechnungen an modellen1

By application of a modified LAOCN-3 program a complete elucidation of the ¹H NMR spectra of 2,3-unsaturated glycosyl phosphonates 1–5 could be achieved. The exactly determined ⁿJ(H, H) and novel ⁿJ(C, P) coupling constants are discussed, and permit a conclusive deduction of the conformations. The ¹³C NMR spectra of 1 to 6 can be fully interpreted. By a close inspection of chemical shifts as well as ¹J(C-H) and ⁿJ(C, P) coupling constants the conformational assignment is supported. For all the derivatives the correlations ¹J(C-1,H_e)>¹J(C-1, H_a) and ¹J(C-1, P_e) >¹J(C-1, P_a) can be used for the assignment of anomers. The crystal structure of 1 is in accordance with this assignment of anomers and displays an unexpected conformation. Calculations by MINDO-3 in resembling model compounds serve to elucidate such conformative effects.     

Synthesis of 2,4-dichlorophenyl methanesulfonate labeled with 14C and 35S

Radioactive 2,4-dichlorophenyl methanesulfonate labeled with ¹⁴C and ³⁵S has been synthesized because it was needed to facilitate the study of the metabolic fate of this interesting nematicide. It was prepared from the reaction between methanesulfonyl chloride and 2,4-dichlorophenol in the presence of a base. Three hundred milligrams of each ¹⁴C- and ³⁵S-2,4-dichlorophenyl methanesulfonate was obtained in a yield of 87% based on ¹⁴C-2,4-dichlorophenol or ³⁵S-methanesulfonyl chloride, respectively. The specific activity was 3.8 mCi/mmol for the compound labeled with ³⁵S and 2.5 mCi/mmol for the ¹⁴C material. Both tracers assayed over 99% after purification.     

Kinetics of O(1D) interactions with the atmospheric gases N2, N2O,H2O,H2, CO2, and O3

Rate coefficients for collisional removal of O(¹D) by six atmospheric gases have been measured by monitoring the appearance of O(³P) following photolytic production of O(¹D). The measured values, k_M±2σ, in units of 10^?11 cm^?3 molecule ^?1 s^?1 are k_O3 = 22.8±2.3, k_N2 = 2.52 ± 0.25, k_CO2 = 10.4 ± 1.0,k_H2O 195± 2.0, k_N2O = 11.7 ± 1.2, and k_H2, = 11.8±1.2.     

Radiometric trace analysis of cobalt with diethyldithiocarbamate-35S,or 203Hg

Two radiometric methods for the determination of submugram amounts of cobalt are described. (A) Cobalt is extracted from an ammoniacal solution with a zinc-diethyldithiocarbamate-³⁵S solution in chloroform. Excess reagent and interfering metals are removed with mercury(II) and cyanide. The ³⁵S in the final organic layer is a measure of the cobalt in this layer. (B) Cobalt is extracted from an ammoniacal solution with a fixed amount of zinc-DDC in chloroform. Excess reagent and complexes of foreign metals are removed by exchange with ²⁰³Hg⁺² and the ²⁰³Hg in the chloroform (compared with a blank) acts as a measure of the cobalt. Method A is applicable to 0.1 μg of cobalt and method B to 0.8 μg. As the efficiency of both processes is variable, isotope dilution with ⁶⁰Co is carried out, A 10-fold excess of foreign metals is permitted in method A and a 4-fold excess in method B ; larger amounts are previously removed, e.g. by extraction with inactive zinc-DDC from sodium hydroxide media.