A comparison of rotational energy accommodation in catalytically produced OD and OH radicals desorbing from a smooth Pt(111) single crystal

1988 ◽  
Vol 88 (1) ◽  
pp. 432-440 ◽  
Author(s):  
David S. Y. Hsu ◽  
M. C. Lin
Keyword(s):  
Single Crystal ◽  
Rotational Energy ◽  
Oh Radicals ◽  
Energy Accommodation

Spectroscopic studies of low-pressure flames; temperature measurements in acetylene flames

1948 ◽  
Vol 194 (1037) ◽  
pp. 169-184 ◽  
Keyword(s):  
Reaction Zone ◽  
Rotational Temperature ◽  
Flame Temperature ◽  
Low Pressure ◽  
Spectroscopic Studies ◽  
Rotational Energy ◽  
Temperature Measurements ◽  
Oh Radicals ◽  
Electronically Excited ◽  
Combustion Processes

Flames at very low pressure haw a relatively thick reaction zone (or flame front) and are especially suitable for detailed study of the combustion processes and of the distribution of energy during the reaction. Temperature measurements have been made, by various spectroscopic methods, on flames of acetylene with air, oxygen and nitrous oxide, in some cases down to a pressure of 1.5 mm. Hg. The excitation temperature has been measured through the reaction zone by the spectrum-line reversal method using Fe, introduced as the carbonyl; the characteristics of the flame containing Fe(CO) 5 are described. The rotational temperature of the excited OH radicals has been determined from the emission spectrum; at pressures above 10 mm. it is fairly constant at around 5700° K, but at lower pressure rises to a higher value of nearly 9000° K. The results are explaihed in terms of the collision and radiative deactivation of the electronically excited OH radicals. These radicals are believed to be formed, as the result of chemical reaction, in the excited 2 Σ state and with a rotational energy equivalent to above 9000° K. Deactivation by collision appears to occur on the average after about forty collisions, if a normal collision diameter is assumed. Removal of electronic excitation occurs mainly by collisions with O 2 molecules, but CO 2 or CO molecules are most effective in removing rotational energy. The variation of concentration of OH through the reaction zone has been determined by its absorption spectrum; it is abnormally high just below the visible reaction zone. Calculations of flame temperature and composition are given. The lack of equipartition of energy is discussed.

A Preparation of High Resolution Standards for Electron Microscopy. Part II

1971 ◽  
Vol 29 ◽  
pp. 160-161
Author(s):  
Akira Tanaka ◽  
David F. Harling
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Carbon Black ◽  
Single Crystal ◽  
Dark Field ◽  
Graphitized Carbon Black ◽  
Graphitized Carbon ◽  
Dark Field Imaging ◽  
Crystal Films ◽  
Micro Holes

In the previous paper, the author reported on a technique for preparing vapor-deposited single crystal films as high resolution standards for electron microscopy. The present paper is intended to describe the preparation of several high resolution standards for dark field microscopy and also to mention some results obtained from these studies. Three preparations were used initially: 1.) Graphitized carbon black, 2.) Epitaxially grown particles of different metals prepared by vapor deposition, and 3.) Particles grown epitaxially on the edge of micro-holes formed in a gold single crystal film.The authors successfully obtained dark field micrographs demonstrating the 3.4Å lattice spacing of graphitized carbon black and the Au single crystal (111) lattice of 2.35Å. The latter spacing is especially suitable for dark field imaging because of its preparation, as in 3.), above. After the deposited film of Au (001) orientation is prepared at 400°C the substrate temperature is raised, resulting in the formation of many square micro-holes caused by partial evaporation of the Au film.

Structure of Palladium Single-Crystal Films Prepared by Flash Evaporation onto (001) NaCl Substrates

1970 ◽  
Vol 28 ◽  
pp. 456-457
Author(s):  
L. E. Murr ◽  
G. Wong
Keyword(s):  
Single Crystal ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
High Rate ◽  
Flash Evaporation ◽  
Optimum Load ◽  
Single Crystal Films ◽  
Crystal Films ◽  
A Current

Palladium single-crystal films have been prepared by Matthews in ultra-high vacuum by evaporation onto (001) NaCl substrates cleaved in-situ, and maintained at ∼ 350° C. Murr has also produced large-grained and single-crystal Pd films by high-rate evaporation onto (001) NaCl air-cleaved substrates at 350°C. In the present work, very large (∼ 3cm2), continuous single-crystal films of Pd have been prepared by flash evaporation onto air-cleaved (001) NaCl substrates at temperatures at or below 250°C. Evaporation rates estimated to be ≧ 2000 Å/sec, were obtained by effectively short-circuiting 1 mil tungsten evaporation boats in a self-regulating system which maintained an optimum load current of approximately 90 amperes; corresponding to a current density through the boat of ∼ 4 × 104 amperes/cm2.

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