Neutralized ionbeam studies of the rare gas hydrides: Observation of unique metastability for NeH J. Chem. Phys. 88, 3116 (1988); 10.1063/1.453955 Observation and characterization of the CH5 radical by neutralized ion beam techniques J. Chem. Phys. 87, 5804 (1987); 10.1063/1.453504 The n=2,3 triplet Rydberg states of the HD molecule observed by fast neutralbeam photofragment spectroscopy J. Chem. Phys. 86, 3050 (1987); 10.1063/1.452010
Experimental observations of excited dissociative and metastable states of H3 in neutralized ion beamsThe N 2 H(D) radical has been studied experimentally by measurement ofthe kinetic energy release in its unimolecular dissociation following formation by electron transfer from metal atoms to high velocity, mass-resolved ion beams and theoretically by ab initio techniques. Calculations ofthe dissociation coordinate of the ground state radical at the MP4/6-311G*"'1 I MP3/6-311G*'" level of theory indicate that the radical is unstable with respect to N2 and H by 0.6 eV but separated from the dissociation products by a 0.4 eV Qarrier. One dimensional tunneling lifetimes are determined to be 7.0X 10-12 s for N2H and 3.6X 10-10 s for N2D.Neutralization of the ion by Zn targets produces predominantly radicals in the 2A I ground state with dissociative lifetimes 1" < 0.5 its, in agreement with the calculations. Mg targets produce the radical in a mixture of the 2 A I ground and 2 A "( 'IT) excited states with a branching ratio dependent on the internal energy of the precursor ion. A higher excited state of the radical, suggested to be an n = 3 Rydberg level, is produced with K targets and is inferred to undergo radiative transitions, probably containing some discrete structure, to the lower 2A I and 2A " ( 'IT) states in the wavelength range of 2700-4500 A. Observations of these transitions may constitute the first spectroscopic observation of the radical.
At room temperature (20" t 3"C), purge and trap samplers provide poor sensitivity for analysis of the fuel oxygenates that are alcohols, such as tertiary butyl alcohol (TBA). Because alcohols are miscible or highly soluble in water, they are not efficiently transferred to a gas chromatograph for analysis. To improve the efficiency of transfer, the water in a purge and trap sampler can be heated. Alternatively, the sensitivity for TBA can be improved by preparing the sample in a heated static headspace sampler. In a heated water sample, the acid used as a preservative may cause chemical hydrolysis of methyl tertiary butyl ether (MTBE) to produce TBA. This effect is well illustrated in this paper using data collected by the U.S. Environmental Protection Agency Office of Research and Development on a plume of MTBE in California. Samples were analyzed using a static headspace sampler heated to 80°C. The ground water samples were preserved in the field with HCl to a pH < 2. The extent of MTBE hydrolysis to TBA during sample analysis varied from 19% to 87%; the average extent of hydrolysis was 59%. To confirm and document the importance of acid hydrolysis of MTBE at higher temperatures during sample preparation, the rate of hydrolysis of MTBE was measured at 80°C. At pH = 1, the rate of hydrolysis was 1.22/h, while the rate at pH = 2 was 0.15h. Acid hydrolysis of MTBE during sample preparation in a heated headspace sampler can be avoided by preserving the sample with 1% (w/w) trisodium phosphate dodecahydrate (TSP) instead of using HCl, or by neutralizing the acid before analysis. In the presence of an acclimated microbial culture, TSP prevented biodegradation of MTBE, as well as benzene, toluene, ethylbenzene, and xylene compounds, in ground water at room temperature for 66 d. However, in a spike recovery experiment, TSP caused based catalyzed hydrolysis of bromomethane. It is not appropriate as a universal preservative. 5030 (US. EPA 1997)-followed by analysis with gas chromatography with a flame ionization detector (EPA Method
The radiologic investigation of asymptomatic hematuria has changed significantly due to the introduction of new imaging modalities and innovative techniques, such as computed tomography urogaphy, which allows a comprehensive evaluation of the entire urinary tract in a single study. There is still a role for "older" imaging modalities, such as intravenous urography and ultrasound, and their use is still advocated in younger patients with a lower risk of malignancy to minimize radiation dose. Combined modality imaging can also be useful for characterization of lesions. Guidelines have recently been published for the radiologic investigation of hematuria; these are discussed in this article.
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