Direct spectroscopic evidence has been obtained indicating that specific OH groups on A1203 and Si02 are consumed as CO interacts with supported Rh crystallites to produce atomically dispersed RhI(CO)2(a). The reaction (1 /x)Rh°* + OH(a) + 2CO(g) -* RhI(CO)2(a) + (l/2)H2(g) has been shown to involve isolated OH(a) groups rather than H-bonded associated OH(a) species. The process may also be reversed upon treatment of the chemisorbed CO layer with H2(g) at temperatures above ~200 K. With the H2 treatment, Rh*(CO)2(a) species are converted back to Rh°* species as judged by changes in the IR spectrum where terminal CO(a) species (on Rh°* sites) and isolated OH(a) groups are regenerated. Comparative kinetic studies of OH(a) and OD(a) species indicate that the rate controlling step in the production of Rh*(CO)2(a) does not exhibit a measurable kinetic isotope effect.

A new design for an infrared cell useful for studies of the spectrum of surface species on high area solids is presented. The cell is well suited over a wide temperature range (100–1000 K). Other demonstrated features of the cell include ultrahigh-vacuum operation, temperature control to ±1 K, linear and rapid temperature programmability and low-temperature gradients across the powdered sample. The method of sample preparation and support minimizes both heat and mass transport effects. A detailed literature search of previous infrared cell designs is included. Results of the application of the new cell design to the high-temperature dehydroxylation of Al2O3 are given as an example of the performance.

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A temperature programmer is presented for use with single crystals and other samples in vacuum. Linear temperature versus time ramps near 100 K and above, and single temperature tracking to ±0.35 K are both achieved with this instrument. A 12-bit digital ramp generator and a digital process controller form the basis of this design. Block diagrams and representative temperature ramps are shown.

(High resolution) electron energy loss spectroscopy [(HR)EELS] has been used successfully to provide direct spectroscopic evidence regarding details of the molecular fragmentation of methoxy (CH3O) on Al(111) caused by energetic electron and ion beams. Chemisorbed methoxy on Al(111) is produced by heating of adsorbed CH3OH. Irradiation of CH3O(a) by either energetic (∼300 eV) electrons or Ar+ ions results in C–O and C–H bond scission with simultaneous formation of Al–O and Al–C bonds. During electron stimulated desorption the CH3O(a) species undergo sequential fragmentation first to CHx groups that are captured by the surface and in the final decay process to adsorbed carbon. C–O bonds in CH3O(a) are depleted preferentially compared to C–H bonds in CHx(a) species. The electron induced sequential fragmentation of the parent CH3 group (from methoxy) to resultant CHx(a) occurs with an efficiency ∼3 orders of magnitude greater then the subsequent process of CHx(a) →C(a). Cross sections for various bond scission processes in electron and ion bombardment have been estimated.