Catalytic Decomposition of H2O(D2O) on a Heated Ir Filament to Produce O and OH(OD) Radicals

Abstract

Production of O atoms, H(D) atoms, and OH(OD) radicals was confirmed in the catalytic decomposition of H 2 O(D 2 O) on a heated Ir filament by laser spectroscopic techniques, such as vacuum-ultraviolet laser-induced fluorescence. The highest steady-state OH density achieved was 2 10 11 cm -3 . The filament temperature dependences of the radical densities were not Arrhenius-type, in contrast to the results on the decomposition of H 2 and O 2 . Especially, OH(OD) density decreased with the increase in the filament temperature over 2100 K. The decomposition process changes from the production of H+OH(D+OD) to that of 2H+O(2D+O) with the increase in the catalysis temperature. This change in the exit channel could not be reproduced by model calculations using the CHEMKIN software package when Arrhenius-type temperature dependences were assumed for the elementary-step rate constants on surfaces. It is necessary to assume that the desorption energy of OH(OD) is surface coverage dependent.

Catalytic decomposition of NH3 on heated Ru and W surfaces

“…The experimental apparatus and the procedure were similar to those described 3 previously [4][5][6][7]. A cylindrical reaction chamber made of stainless steel, 10 cm in internal diameter, was used.…”

“…H atoms produced on heated wires were detected by a vacuum-ultraviolet (vuv) laser absorption technique and a vuv laser-induced fluorescence (vuv LIF) technique at 121.6 nm [5][6][7]. The distance between the wire and the detection zone was 9 cm.…”

“…Mass spectrometric analysis was also carried out to measure the decomposition efficiency [4][5][6][7]. A quadrupole mass-spectrometer was attached to the chamber through a sampling hole (0.1 mm in diameter).…”

Gas-phase diagnoses in catalytic chemical vapor deposition (hot-wire CVD) processes

“…When we detect molecular radicals, such as SiH, NH, OH, and PH, the radiative lifetimes of the excited states are usually much longer than the duration time of nanosecond laser pulses and spontaneous radiation during the laser pulse can be ignored [30,34,36,37,39,61]. After the laser pulse, these systems cannot be regarded as two-level ones, but that does not matter unless the fluorescence is highly dispersive.…”

“…Shown in Fig. 1 is an LIF spectrum of OH formed from H 2 O on a heated Ir wire and a simulated one [37]. These spectra correspond to the (0,0) band of the A 2 Σ + -X 2 Π transition.…”