Optical double-resonance spectroscopy of trapped Cs atoms: hyperfine structure of the 8s and 6d excited states

Transitions between excited states of Cs atoms prepared in a magneto-optical trap are investigated with a two-step excitation process. The first step is provided by the trapping laser radiation, the second step to higher excited states is done with an additional laser. We measure the hyperfine structure of the 8s and 6d states and investigate the effect of the relevant trap parameters on the accuracy of the data.     

Physico-chemical properties of deuteriated compounds. 6th Communication. The H/D exchange in mixtures between hydrogen and heptane,methylcyclohexane or cycloheptane over Ni-catalyst

The isotopic exchange between hydrogen and saturated hydrocarbons over Nicatalysts has been studied as a function of temperature and degree of deuteriation. The experimental results can be explained by a model containing four parameters. Two different adsorbed species are assumed: in the ‘alkyl’-species one H-atom is exchanged in a single adsorption step; the ‘olefin’-species exchanges at least two H-atoms at the same time. Both species can undergo multiple exchange per adsorption step.     

Structure and fragmentation of [C3H7O]+ ions formed by chemical ionization

The unimolecular metastable and collision-induced fragmentation reactions of [C₃H₇O]⁺ ions produced by gas-phase protonation of acetone, propanal, propylene oxide, oxetan and allyl alcohol have been studied. The CID studies show that protonation of acetone and allyl alcohol yield different stable ions with distinct structures while protonation of propanal or propylene oxide yield [C₃H₇O]⁺ ions of the same structure. Protonated oxetan rearranges less readily to give the same structure(s) as protonated propanal and propylene oxide. The [C₃H₇O]⁺ ions fragmenting as metastable ions after formation by CI have a higher internal energy than the same ions fragmenting after formation by EI. Deuteronation of the C₃H₆O isomers using CD₄ reagent gas shows that loss of C₂H₃D proceeds by a different mechanism than loss of C₂H₄. The results are discussed in terms of potential energy profile for the [C₃H₇O]⁺˙ system proposed earlier.     

Hyperfine structure and isotope shift of the 3s-3p transitions of atomic oxygen

Using high-resolution saturation spectroscopy, by means of both double heterostructure and multiple quantum-well AlGaAs diode lasers, we investigate the isotope shifts and the hyperfine structure in the 3s-3p transitions of the triplet and quintet systems of atomic oxygen. From the analysis of the signals from¹⁷O we can deduce precise values for the hyperfine structure magnetic dipole constants. A theoretical analysis allows us to bring into evidence core polarization effects in the hyperfine structure. By heterodyning two frequency locked lasers, we perform a direct frequency measurement of the isotope effect on the³ S ₁→³ P _1,2,0 transitions. From the comparison with similar accuracy data on the corresponding quintet transitions, an upper bound to the size of the nuclear volume effect is given, and precise values for the specific mass contributions are consequently obtained.     

The Mass Spectrometric Fragmentation of 1-Heptyl Ions Derived from the Corresponding Halides

We have studied the fragmentation of 1-heptyl ions resulting from the loss of halogen from the corresponding halide ions. All positions had been labelled with D and ¹³C, some positions even doubly labelled. The main processes are the loss of propene and, to a lesser extent, ethylene as neutral fragments. All carbon atoms have a definite probability of being lost with the olefin, those which are terminal having the smallest chance; this precludes an important contribution by direct scission. The source-and the metastable-decomposition produced much the same isotopic distribution in the fragments. The terminal hydrogen atoms also have a small chance of being rearranged, whereas those at non-terminal positions show extensive scrambling. It seems that the fragmentation proceeds via cyclic structures which are rapidly attained and equilibrated amongst each other, but our results do not warrant suggestion of a detailed model.     

The Chemical Ionization of Organic Compounds. 2nd Communication. Linear Alkyl Halides

The chemical ionization spectra of linear alkyl halides with up to nine carbon atoms have been studied using water as protonating agent. An alkyl ion with the same number of carbon atoms as the halide is produced. With more than six carbon atoms in the chain, fragmentation becomes important. The results show that excited hydronium ions participate as intermediates and the fragments of the resulting alkyl ions have branched structures.     

Strahlungschemie von Kohlenwasserstoffen. 17. Mitteilung. Hexan-NO

The influence of NO on the radiolysis of hexane at ?70°C has been studied. The results allow the following interpretations: The bimolecular part of the hydrogen production is in contrary to N₂O efficiently quenched by NO. This part involves non-thermal hydrogen atoms and has a G-value of about 1.4. All olefins are suppressed, probably in a secondary chain reaction with NO. The radical yield is drastically reduced by very low concentrations of NO, but by higher concentrations this decrease is slowed down. A reaction scheme proposed by BURRELL is able to explain these results.     

Physico-Chemical Properties of Deuteriated Compounds. 2nd Communication. The isotope partition coefficient in methylcyclohexane-hydrogen

The deuterium isotope partition coefficient α has been determined as a function of total pressure, temperature and degree of deuteriation for methylcyclohexane/hydrogen over Ni/Al₂O₃. Good agreement with theory has been obtained for the dependence on temperature but not for that on total pressure or on the degree of deuteriation.     

A continuous cold atomic beam from a magneto-optical trap

We have developed and characterized a new method to produce a continuous beam of cold atoms from a standard vapour-cell magneto-optical trap (MOT). The experimental apparatus is very simple. Using a single laser beam it is possible to hollow out in the source MOT a direction of unbalanced radiation pressure along which cold atoms can be accelerated out of the trap. The transverse cooling process that takes place during the extraction reduces the beam divergence. The atomic beam is used to load a magneto-optical trap operating in an ultra-high vacuum environment. At a vapour pressure of 10^-8mbar in the loading cell, we have produced a continuous flux of 7×10⁷atoms/s at the recapture cell with a mean velocity of 14 m/s. A comparison of this method with a pulsed transfer scheme is presented. Received 19 February 2001