scholarly journals Femtosecond time-resolved photodissociation dynamics of methyl halide molecules on ultrathin gold films

2011 ◽  
Vol 2 ◽  
pp. 618-627 ◽  
Author(s):  
Mihai E Vaida ◽  
Robert Tchitnga ◽  
Thorsten M Bernhardt
Keyword(s):  
Methyl Iodide ◽  
Methyl Bromide ◽  
Uv Light ◽  
Strong Dependence ◽  
Methyl Chloride ◽  
Gold Surface ◽  
Rapid Quenching ◽  
Negative Ion ◽  
Time Resolved ◽  
Methyl Halide

The photodissociation of small organic molecules, namely methyl iodide, methyl bromide, and methyl chloride, adsorbed on a metal surface was investigated in real time by means of femtosecond-laser pump–probe mass spectrometry. A weakly interacting gold surface was employed as substrate because the intact adsorption of the methyl halide molecules was desired prior to photoexcitation. The gold surface was prepared as an ultrathin film on Mo(100). The molecular adsorption behavior was characterized by coverage dependent temperature programmed desorption spectroscopy. Submonolayer preparations were irradiated with UV light of 266 nm wavelength and the subsequently emerging methyl fragments were probed by photoionization and mass spectrometric detection. A strong dependence of the excitation mechanism and the light-induced dynamics on the type of molecule was observed. Possible photoexcitation mechanisms included direct photoexcitation to the dissociative A-band of the methyl halide molecules as well as the attachment of surface-emitted electrons with transient negative ion formation and subsequent molecular fragmentation. Both reaction pathways were energetically possible in the case of methyl iodide, yet, no methyl fragments were observed. As a likely explanation, the rapid quenching of the excited states prior to fragmentation is proposed. This quenching mechanism could be prevented by modification of the gold surface through pre-adsorption of iodine atoms. In contrast, the A-band of methyl bromide was not energetically directly accessible through 266 nm excitation. Nevertheless, the one-photon-induced dissociation was observed in the case of methyl bromide. This was interpreted as being due to a considerable energetic down-shift of the electronic A-band states of methyl bromide by about 1.5 eV through interaction with the gold substrate. Finally, for methyl chloride no photofragmentation could be detected at all.

scholarly journals The kinetics of certain reactions between methyl halides and anions in water

1949 ◽  
Vol 196 (1047) ◽  
pp. 540-553 ◽  
Keyword(s):  
Dipole Moment ◽  
Methyl Iodide ◽  
Methyl Bromide ◽  
Methyl Chloride ◽  
Polar Molecules ◽  
Methyl Halides ◽  
Methyl Halide ◽  
Kinetics Of ◽  
Chloride Methyl

The rates at which methyl chloride, methyl bromide and methyl iodide react with the hydroxyl and the thiosulphate ions in water have been measured at various concentrations and temperatures. The apparent energies of activation in both series increase in the same direction as the dipole moment of the methyl halide. The results are discussed in terms of a theory of the kinetics of the reactions between ions and polar molecules in solution.

scholarly journals Strain IMB-1, a Novel Bacterium for the Removal of Methyl Bromide in Fumigated Agricultural Soils

1998 ◽  
Vol 64 (8) ◽  
pp. 2899-2905 ◽  
Author(s):  
Tracy L. Connell Hancock ◽  
Andria M. Costello ◽  
Mary E. Lidstrom ◽  
Ronald S. Oremland
Keyword(s):  
Methyl Iodide ◽  
Methyl Bromide ◽  
Agricultural Soils ◽  
Treatment Strategies ◽  
Methyl Chloride ◽  
Methylotrophic Bacterium ◽  
Rrna Gene ◽  
Low Concentrations ◽  
Novel Bacterium ◽  
Bacterium Strain

ABSTRACT A facultatively methylotrophic bacterium, strain IMB-1, that has been isolated from agricultural soil grows on methyl bromide (MeBr), methyl iodide, methyl chloride, and methylated amines, as well as on glucose, pyruvate, or acetate. Phylogenetic analysis of its 16S rRNA gene sequence indicates that strain IMB-1 classes in the alpha subgroup of the class Proteobacteria and is closely related to members of the genus Rhizobium. The ability of strain IMB-1 to oxidize MeBr to CO2 is constitutive in cells regardless of the growth substrate. Addition of cell suspensions of strain IMB-1 to soils greatly accelerates the oxidation of MeBr, as does pretreatment of soils with low concentrations of methyl iodide. These results suggest that soil treatment strategies can be devised whereby bacteria can effectively consume MeBr during field fumigations, which would diminish or eliminate the outward flux of MeBr to the atmosphere.

The Treatment of Some Cyclic Thiocarbonates With Methyl Halide/Propylene Oxide

1987 ◽  
Vol 40 (5) ◽  
pp. 795 ◽  
Author(s):  
JJ Patroni ◽  
RV Stick
Keyword(s):  
Propylene Oxide ◽  
Methyl Bromide ◽  
Methyl Chloride ◽  
Product Distributions ◽  
Methyl Halide

Treatment of thiocarbonates (OCSO) with methyl iodidelpropylene oxide at 80� can lead smoothly to the carbonate. In some cases, a competing process is the formation of iodo thiocarbonates ( OCOSMe ), and an explanation is provided for the product distributions observed. The corresponding reactions with methyl bromide and methyl chloride (as methyl chloroformate ) are much less efficient.

Isotopic Characterization (2H, 13C, 37Cl, 81Br) of the Abiotic Sinks of Methyl Bromide and Methyl Chloride in Water and Implications for Future Studies.

2018 ◽  
Author(s):  
Axel Horst ◽  
Magali Bonifacie ◽  
Gérard Bardoux ◽  
Hans-Hermann Richnow
Keyword(s):  
Methyl Bromide ◽  
Isotope Fractionation ◽  
Methyl Chloride ◽  
Methyl Halides ◽  
Future Studies ◽  
Halide Exchange ◽  
Isotopic Characterization

In this study we investigated the isotope fractionation of the abiotic sink (hydrolysis, halide exchange) of methyl halides in water.<br>

Electro-optical property of polymerized liquid crystal devices using linearly polarized UV irradiation

2021 ◽  
Author(s):  
Masahiro Ito ◽  
Kazuma Kajiwara ◽  
Kohki Takatoh
Keyword(s):  
Liquid Crystal ◽  
Uv Light ◽  
Strong Dependence ◽  
Fast Response ◽  
Alignment Layer ◽  
Liquid Crystal Devices ◽  
Decay Times ◽  
Linearly Polarized ◽  
Reactive Mesogens ◽  
Strong Anchoring

Abstract Display characteristics have a fairly strong dependence on the configuration of the liquid crystal (LC) molecules and interactions between the LC molecules and the alignment layer surface. To obtain LC devices with a fast response, the usage of reactive mesogens (RMs) have been studied. RMs polymerize in the vicinity of the alignment layer. We assessed the effectiveness of linearly polarized UV light for polymer formation. Three kinds of UV light, namely (i)non-polarized (ii)parallel to, and (iii)perpendicular to the rubbing direction, were used to irradiate LC cells with RM concentrations of 5wt% and 10wt%. For both RM concentrations, LC devices using LPUV parallel to the rubbing direction yielded the shortest decay times. SEM observation revealed that the fibrils polymerized linearly in the same direction on using LPUV parallel to the rubbing direction. The decay time was presumably shortened by the strong anchoring force and high alignment ability of the linear fibrils.

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