Husain studies

Because anhydrous nitric acid is of low thermal stability even at room temperature, very few photochemical and radiolytic studies have been carried out with it. A flash photolytic study of nitric acid vapour by Husain and Norrish250 has provided evidence for a primary photochemical split into OH and N02, viz. 

Husain, L., and V. A. Dutkiewicz, A Long-Term (1975-1988) Study of Atmospheric S04 Regional Contributions and Concentration Trends, Atmos. Environ., 24A, 1175-1187 (1990). 

Time-resolved emission from I2(fi3n0u+) has been studied in a static system by Abrahamson, Husain, and Wiesenfeld23 following the flash photolysis of CF3I. The basis of the mechanism giving rise to the emission may be written ... 

O( D) + Chlorojluoromethones. The reactions of O( D) with chloro-lluoromethanes have been studied by Donovan et al. (316), Gillespie and Donovan (396), and Fletcher and Husain (362). The reactions yield predominantly CIO radicals... 

The Br(2P1/2) state lies 0.456 eV above the ground 2P3/2 state and is meta-stable with a lifetime of 1.12 sec. The Br(2P,/2) atoms can be detected by absorption at 1532, 1582, and 1634 A. The Hash photolysis in the vacuum ultraviolet of HBr, Br2, CHCl2Br, and CF3Br has produced Br(2P,/2) atoms that have been observed by optical absorption [Donovan and Husain (299)]. The quenching efficiency of Br(2P1/2) produced from the Hash photolysis of CF3Br by various gases has been studied by Donovan and Husain (300). 

The ground state C atoms are produced by the photolysis of carbon suboxidc. They can be monitored by optical absorption at 1657 A. Reactions of C(3P) atoms with molecules have been studied by Husain and Kirsch (497,498) and Braun et al. (141). 

Preliminary studies in our laboratory with orcinol hydroxylase, from a pseudomonad, suggested that the 1-dFAD-reconstituted enzyme would catalyze NADH oxidation, but 02 was reduced exclusively to H202. No oxygen transfer yielding trihydroxytoluene could be detected. Because of instability of both trihydroxytoluene oxygenation product and orcinol hydroxylase apoenzyme, the 1-dFAD studies were pursued next in collaboration with Massey, Husain, Ballou, and Entsch at University of Michigan with the most well characterized bacterial flavoenzyme hydroxylase, p-hydroxybenzoate hydroxylase (2, 26, 27). The apoenzyme was reconstituted stably with 1-deazaFAD... 

Several studies have demonstrated the improved stability of peroxidases when they were subjected to immobilization. Akhtar and Husain observed that bitter gourd peroxidase (BGP) was able to remove higher percentage of phenols over a wider range of pH when immobilized on a bioaffinity support [37]. Sasaki et al. highlighted an improvement of thermal stability of MnP immobilized on FSM-16 mesoporous material [59]. Furthermore, some other studies demonstrated a protective effect of peroxidase immobilization against inactivation by H202 [7, 20]. The different behavior of immobilized peroxidases with respect to soluble ones points out the necessity of an optimization of the process conditions when immobilized enzyme is used. Nevertheless, the possible improvement in stability should balance the usual decrease in kinetic rates, due to substrate transfer limitations to reach the enzyme inside the support. 

The deactivation of OCD2) by halocarbons has been studied in a number of laboratories and both the overall kinetics and reaction mechanisms quite thoroughly examined (Fletcher and Husain, 1976 Davidson ei al., 1978 Force and Wiesenfeld, 1981). Both quenching and reaction play significant roles here, although reaction dominates except in the cases of CF4 and CHFi. Electrophillic attack upon the chlorine atom may well dominate deactivation of O ( D2) by the chloro-carbons (Addison et al., 1979). Molecular elimination of hydrogen halides as in... 

Arrowsmith et al used the crossed beam reaction F+Na— NaF+Na (3 P) to study radiative transfer and electronic energy transfer (E — E, V) in the Na (3 P)-1-NajCX S ) system. Previous studies of the Na2 system have utilized high-pressure cells or heat pipes in which radiation trapping is strong and Na + Na2 collisional energy transfer dominates. Time-resolved emission, following pulsed dye-laser excitation, has been used by Husain and his coworkers in a systematic survey of the excited-state behaviour of Mg(3 Pj), Ca(4 P,), and Sr(5 Pj). Dye-laser excitation of Mg vapour at 457.1 nm resulted in the observation of slow spontaneous emission from Mg(3 P,) which... 

An important series of studies on the pyrolysis and oxidation of both ammonia and hydrazine was published by Husain and Norrish in 1963. These workers studied both systems by the method of flash photolysis and kinetic spectroscopy developed in Norrish s laboratory over a decade earlier. The major observations in the oxidation of NH3 were (1) the NH3-O2 explosion is preceded by an induction period of several milliseconds, at the end of which the spectra of NO, O2, and OH are observed in vibrationally excited states (but with a vibrational temperature equal to the translational temperature) (2) NH and OH spectra are observed before the end of the induction period and (3) the main nitrogenous product is NO, with some N2O. 

Further support for the Husain and Norrish mechanism comes from the work of Bradley et They studied the shock oxidation of NH3 at total pressures... 

The lack of laser action in the photolysis of isopropyl iodide raises intriguing questions. As Husain and Donovan point out, this does not necessarily indicate the absence of population inversion, since under the laser experimental conditions there could instead be an insufficient absolute concentration of I atoms. Spectroscopic studies show that excited iodine atoms are produced from isopropyl iodide photodissociation, but at lower relative concentrations than for n-propyl iodide under similar conditions. Since the two propyl iodides show similar I quenching rates, it would appear most likely that a decreased I /I ratio is the reason stimulated emission is not seen. The present experiments, unfortunately, cannot provide a more quantitative explanation. The distinct broadness of the isopropyl iodide distribution in fig. 2 indicates a departure from the methyl- ethyln-propyl trend, and might represent comparable amounts of P and I atom production, with overlapping translational energy distributions, at least when viewed with our present... 

Other photolysis studies have been reported for ethyl iodide -propyl iodide and isopropyl iodide in the gas phase, and also in liquid and solu-tion . Solution and liquid phase studies have also been reported for butyl ° , pentyl and cetyl iodides ". The primary process in the photolysis of alkyl iodides has been further discussed by Donovan and Husain in reference to the formation of excited halogen atoms. 

Ting and Weston (973) have studied reactions of CH3 radicals produced by the photolysis of CHsBr al 1849 A. The CH3 radicals thus formed have been found to carry an excess energy sufficient to overcome the activation energy for the H atom abstraction from CH3Br or Hj. Only Br( P3,2) has been delected in the vacuum ultraviolet photolysis of CH Br [Donovan and Husain (299)]. Very recent results by Shold and Rebbcrt (873a) indicate that CH3CI dissociates into CHjCI -f H, CH2 + HCl and CHCI -f H2 as well as (VII-125) at 1470 and 12.36 A. 

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