George W. Coulston

The dynamics of CO oxidation on Pd, Rh, and Pt studied by high-resolution infrared chemiluminescence spectroscopy

The dynamics of carbon monoxide oxidation on Pd, Rh, and Pt foils were probed under nearly collision‐free conditions using high resolution infrared chemiluminescence. Auger electron spectroscopy was used to verify the absence of impurities on the surfaces. The reactants were supplied to the surface through a free jet nozzle source, while a Fourier transform infrared spectrometer operating at 0.012 cm−1 resolution was used to fully resolve the rotational structure of several vibrational transitions in the product CO2 (22 in the case of Pd). In all cases, the product CO2 is vibrationally excited and the apparent vibrational temperatures are in the same order as the peak reaction rates, i.e., Pd>Pt>Rh. The surface coverage of oxygen on Pd was varied by changing the CO: O2 ratio and the surface temperature and, in both cases, increasing oxygen coverage causes an increase in vibrational excitation of product CO2. On Pt and Rh, the apparent temperatures of different vibrational modes are similar, while on Pd, t...

Population transfer by stimulated Raman scattering with delayed pulses: Analytical results for multilevel systems

Stimulated Raman scattering involving adiabatic passage (STIRAP) is a proven technique for population transfer in three‐level systems with strong oscillator strengths. We show that the STIRAP process should also yield high transfer efficiencies when the densities of states near the intermediate and final levels are high, provided certain criteria for the experimentally controllable parameters are met. We also show that high transfer efficiencies may even be possible when the pump and Stokes lasers can access levels outside of the three‐level system. The criteria are derived with an approach that emphasizes the adiabatic nature of the transfer process in an eigenvector of the interaction Hamiltonian that resembles a trapped state. The results are compared to density matrix calculations.

Population transfer by stimulated Raman scattering with delayed pulses using spectrally broad light

The feasability of selective and complete population transfer between atomic or molecular levels by stimulated Raman scattering with delayed pulses involving spectrally broad light with characteristics typical for pulsed lasers is investigated. In extension of previous work, the effect on the transfer efficiency of phase fluctuations and of the detuning ΔR of the laser frequencies from the two‐photon resonance is analyzed. The minimum pulse energy Pmin required to achieve a transfer efficiency of nearly unity is derived analytically, with some restrictions imposed on the type of phase fluctuations. Pmin increases approximately proportional to the square of the bandwidth of the laser radiation and to the square of ΔR. The conclusions are confirmed by the results of extensive numerical calculations. These studies also reveal a high sensitivity of the transfer efficiency to the autocorrelation of the fluctuating light.

The effect of vibrational excitation (3≤v‘≤19) on the reaction Na2 (v‘)+Cl→NaCl+Na*

The variation of the total integral cross section for the chemiluminescent channel with the vibrational excitation 3≤v‘≤19 is investigated using laser‐induced fluorescence or coherent population transfer, a new method employing delayed interaction with two cw lasers to populate vibrationally excited levels. The cross section increases with v‘ by about 0.76% per vibrational level. The results are in agreement with the results of phase‐space calculations, as well as with those from simple curve crossing models.

Direct measurement of vibrational level populations in CO2 produced during CO oxidation on Pd

The dynamics of carbon monoxide oxidation by O2 on a Pd foil were probed under nearly collision free conditions using high resolution infrared chemiluminescence. Auger electron spectroscopy was used to verify the absence of impurities on the Pd surface. The reactants were supplied to the surface through a free jet nozzle source while a Fourier transform infrared spectrometer (Bomem DA3002) operating at 0.012 cm−1 resolution was used to fully resolve the rotational structure of 14 vibrational transitions in the product CO2. It was found for reaction on a 600 K surface that the (1001, 2001, 3001) symmetric stretch levels were populated consistent with an apparent vibrational temperature of Tsymmetric=3150 K. However, the populations of the levels with no symmetric component (0001, 0111, 0201, 0221, 0311, 0331, 0002, 0401, 0421, 0441, 0003) were better characterized by a temperature Tnonsymmetric=1900 K, with individual mode temperatures for bending and antisymmetric stretch being equal to 1820 and 2130 K, r...

Dynamics of Heterogeneously Catalyzed Reactions

A mechanism may be postulated on several levels of sophistication [1]. In its most rudimentary form, a mechanism of a heterogeneous reaction is a sequence of elementary steps that accomplishes the overall reaction. For example, the mechanism of CO oxidation on Pt may be written [2]:

Elementary Reaction Steps in Heterogeneous Catalysis: A Workshop Overview

{\rm{CO}}({\rm{g}}) \leftrightarrow {\rm{CO}}({\rm{ad}})

SUPPORTED VPO CATALYSTS FOR SELECTIVE OXIDATION OF BUTANE. II. CHARACTERIZATION OF VPO/SIO2 CATALYSTS

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