Yaser A. Yousef

Ab Initio calculations of the stabilization energies of the conformational and the structural isomers of C3H7X where X = F, Cl, and Br

HF, MP2, and B3LYP calculations with different basis sets have been used in the computation of the stabilization energies of C3H7X isomers, where X is F, Cl, and Br. The experimental stabilization energies of the structural isomers of C3H7Cl and C3H7Br have been reproduced via B3LYP calculations. However, the calculated stabilization energies of fluoropropane isomers from their reported enthalpies of formation have been reproduced in all methods of calculations in present work. The experimental relative stabilities of the gauche conformers of 1‐fluoro‐, 1‐chloro‐, and 1‐bromopropanes have been also reproduced via some of the used calculations in the present work. The effect of the geminal interactions on X atomic charges and on the C–X and C–C bond lengths in halopropane isomers are also discussed.

Photodegradation of Carbaryl in Acetonitrile Solution

Abstract The photochemical decomposition, induced by UV radiation, of the carbamate pesticide (Carbaryl) in acetonitrile has been examined by means of gas chromatography–Mass spectrometry (GC‐MS). The result of continuous irradiation was almost total degradation of the pesticide examined. In order to investigate the nature of the reaction products, a spectroscopic study (UV‐Vis, steady‐state fluorescence, and fluorescence lifetime) of the products was performed. Phthalic anhydride and traces of 1,4‐naphtalenedione as an intermediate were detected as reaction products. The presence of a trace amount of 1‐naphthol as one of the photoproducts was confirmed by fluorescence lifetime measurements.

Decay Lifetimes of Para-Substituted Polystyrene in Solid Films and in Dichloromethane

The fluorescence decay times of polystyrene, poly(4-bromostyrene), poly(4-chlorostyrene), poly(4-methylstyrene), poly(α-methylstyrene), poly(4-methoxystyrene), and poly(4-tert butylstyrene) were measured in solid films and in dichloromethane solution. A detailed analysis of the emission profile performed by nanosecond time resolved fluorescence spectroscopy confirmed the presence of monomer fluorescence as well as excimer fluorescence in both media. Monomer fluorescence decay times gave shorter times compared with that of excimer decay times in dichloromethane solution. Fluorescence from substituted polystyrene was mainly excimer fluorescence with shift of maximum emission to longer wavelength. The ratio of monomer to excimer contributions was found to be dependent on the emission wavelength, but was not affected by polymer concentration. Both monomer and excimer fluorescence lifetimes as well as excimer intensity increase with increasing emission wavelength. An accompanying decrease in monomer contribution is also observed is solution in comparison with that in solid films.

Photodegradation of α-Tocopheryl Acetate Using Nanosecond Laser Pulses Obtained from the 4th Harmonic Output of Nd-YAG Laser

The aim of this study was to investigate the effect of ultra-fast UV laser pulses on the photostability of -tocopheryl acetate (vitamin e acetate) in hexane. UV-Vis absorption and fluorescence spectra of vitamin e acetate and vitamin e in three types of solvents, namely methanol, acetonitrile and hexane, are presented. UV-Vis spectrophotometry was used to follow the photodegradation kinetics of the molecule in hexane. The photodegradation was found to follow first order kinetics. Degradation photoproducts were separated by TLC and identified by mass spectroscopy.

Excited State Structural Changes of 10-Cyano-9-tert-butyl-anthracene (CTBA) in Polymer Matrices

Two main deactivation processes are suggested to be present in the electronic excited state of 10-cayano-9-tert-butyl-anthracene (CTBA): one leading to the Dewar strucure resulted from photochemical effect, similar to the case of 9-tert-butyl-anthracene (TBA), which is enhanced in solution, and another leads to a more planar structure leading to a Charge Transfer (CT) state and is enhanced in polymers. The presence of donor (tert-butyl group) and an acceptor (cyano group) along the line of 9,10 positions in CTBA confirm our hypothesis of CT state. Our suggestions were supported by steady state and time resolved fluorescence spectra results.

Photolysis of Some Benzimidazole Based Pesticides

The need for increased food production and control of disease vectors brought about a major development in the area of pest control (Martin, H., 1971). Public concern about pesticide contamination only became apparent after the publication of the biologist Rachel Carson (Johnson, D. 1968). This concern has generated a large number of studies in all aspects of pesticide research, including the possible effects and extent of environmental pollution (Tweedy, B. et al, 1968; Johnson, D. 1968). Gaetano Rango... et al, studied the photo and thermal degradation of Albendazole, Fenbendazole and Mebendazole. They found that all drugs showed high photosensitivity in solution but a reliable stability in solid form and when exposed to a temperature up to 50 °C. Photolysis was found to cause demethylation or decarboxylation of the parent compounds (Gaetano R., et al., 2006). Abdou M., ... et al, studied the effect of singlet oxygen on the photostability of Carbendazim in aqueous hydrochloric acid. They could identify some of the photoproducts such as the brownish colored insoluble dimer of benzimidazole (Abdou M. et al., 1986). Boudina A. et al, investigated the quantum efficiency of carbendazim in aqueous solution and the effect of pH value on the photostability of the pesticide. They suggested a possible phtodegradation mechanism and proposed a final photoproduct using HPLC and GC-MS analytical techniques. Monocarbomethoxy-guanidine was the most stable photoproduct (Boudina A. et al., 2003). Saien J. and Khezrianjoo studied the kinetic photodegradation of carbendazim in the presence of TiO2 catalyst (Saien J., and Khezrianjoo S. 2008). Fluorescence quantum yield of Carbendazim in aqueous solution at 254 nm was determined by Mazellier et al, (Mazellier P. et al. 2002). The benzimidazole fungicides have been shown to be outstanding agents in disease control (Mazellier P. et al. 2002; Fleeker J. and Lacy H., 1977). They are used in the Jordanian agricultural valley where harsh weather conditions are known to exist. Although, such molecules are known to be stable towards solar radiation, the solar spectral distribution in the Jordanian valley extends down to 280 nm where photons in this range of wavelength can be absorbed by such molecules (Yousef A. et al., (2007). Therefore, focusing on the effect of UV light on these molecules can be considered an important agricultural and environmental aspect to that area.

Influence of a nanosecond pulsed laser on aluminium alloys: Distribution of oxygen

Nanosecond laser pulses may produce both thermal melting (as femtosecond and picosecond pulses) or ultrafast nonthermal melting depending on the pulse fluence. This was demonstrated experimentally by Sokolowski-Tinten et al. [1], who found that the transformation of GaAs into its liquid state occurs within several tens of picoseconds at fluences close to the melt threshold due to thermal melting under highly superheated conditions or within several hundred femtoseconds via carrier excitation for very high fluences. The processes occurring under high energetic fs pulse irradiation could be described more precisely with the help of the theoretical work of Stampfli et al. In this work, a nanosecond pulsed laser (Nd:Yag) is used to irradiate an aluminum alloy sample. The oxygen distribution is studied as a function of distance in order to get an idea about the temperature distribution.