Laser halogens

In an excimer laser the mixture of inert gas, halogen gas, and helium, used as a buffer, is pumped around a closed system consisting of a reservoir and the cavity. 

The material evaporated by the laser pulse is representative of the composition of the solid, however the ion signals that are actually measured by the mass spectrometer must be interpreted in the light of different ionization efficiencies. A comprehensive model for ion formation from solids under typical LIMS conditions does not exist, but we are able to estimate that under high laser irradiance conditions (>10 W/cm ) the detection limits vary from approximately 1 ppm atomic for easily ionized elements (such as the alkalis, in positive-ion spectroscopy, or the halogens, in negative-ion spectroscopy) to 100—200 ppm atomic for elements with poor ion yields (for example, Zn or As). 

Si3N4 powder by laser CVD from halogenated silane and ammonia with an inert sensitizer such as SFg.P l... 

Bauer,R., Smulders,R, Geus,E., vanderPut, J., and Schoomman, J., Laser Vapor Phase Synthesis of Submicron Silicon and Silicon Nitride Powders from Halogenated Silanes, Ceram. Eng. Sci. Proc., 9(7-8) 949-956(1988)... 

Photothermal sensitization has been mentioned briefly with regard to nickel(II) octabutoxy-naphthalocyanine (Section 9.22.10.1). A similar phenomenon has been observed with copper(II) haematoporphyrin ((1), Cu for 2H).196 This substance is accumulated by amelanotic melanoma cells. When the impregnated cells were subjected to light from a quartz-halogen lamp cell survival was not affected (i.e., no PDT effect), but intense pulsed laser irradiation (532 nm, Q-switched... 

Laser flash photolysis at wavelengths within the charge-transfer absorption bands of 2,2,6,6-tetramethylpiperidine-./V-oxyl (TEMPO) and carbon tetrachloride yields theoxoam-monium chloride of TEMPO 291 (Xmax = 460 nm) and the trichloromethyl radical in an essentially instantaneous 18 ps) process152. The primary photochemical reaction is an electron transfer from TEMPO to carbon tetrachloride followed by immediate decomposition of the carbon tetrachloride anion radical to chloride and trichloromethyl radical (equation 140). The laser flash photolysis of TEMPO and of other nitroxides in a variety of halogenated solvents have confirmed the generality of these photoreactions152. 

An alternative LIS scheme is one in which a vibrationally excited molecule reacts preferentially with another species. An example is the hydrogen halide/olefin addition reaction, DX + RiR2C = CH2 RiR2CXCH2D. The scheme involves sequential absorption of several quanta from a C02 laser near 5 p,m to selectively excite DX to a vibrational quantum number of 3 or more. Successful implementation would be expensive because of the highly corrosive nature of halogen acids. 

Resonance Raman effects in halogen gases have been observed by Holzer etal. 207a). with an appropriate choice of exciting lines from an argon laser either resonance Raman effect or resonance fluorescence could be observed. The difference between the two spectra is discussed. In the case of a strong resonance Raman effect, overtone sequences up to the 14 harmonic could be observed. 

The toxicities of those perhalogenated iodoalkanes used in industrial telomerization processes, in laser-based nucleus fusion research and for other applications have been published in some detail (Table 16). The short chain linear perfluoroiodoalkanes are nontoxie. Branching of the carbon backbone and lower bond strength of the halogens involved are responsible for higher biological activity, observed in some cases. The higher linear perfluorinated iodoalkanes are completely inert materials. 

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