The absolute rate coefficient of the gas-phase reaction HCCO+O2 was determined over the temperature range 296–839 K and at a pressure 7±1 Torr helium. The experiments were performed in a slow-flow kinetic apparatus employing pulsed photolysis of CH2CO at 193 nm as a source of HCCO radicals. Reaction time profiles of [HCCO] were constructed using a newly developed, sensitive spectroscopic technique in the visible spectral region to detect this radical: laser—induced fluorescence of nascent CH(X 2Π) photofragments following HCCO photodissociation at 266 nm. Photodissociation of HCCO at this wavelength was found to produce rotationally excited CH(X) populated to N″⩾26. The rate coefficient for the title reaction was found to be described by k(T)(HCCO+O2)=(2.6±0.3)×10−12 exp[−(325±80)K/T] cm3 s−1 molecule−1 (2σ errors). The absorption cross section of HCCO at 266 nm, σHCCO(266 nm), was also determined relative to that of CH2CO at 193 nm as σHCCO(266 nm)=0.07−0.05+0.20σCH2CO(193 nm).

The absolute rate coefficient of the gas-phase reaction HCCO + NO was experimentally determined for the first time over an extended temperature range, 297-802 K. HCCO radicals were generated by pulsed-laser photolysis of CH 2 CO at 193 nm. Their subsequent decay, under pseudo-first-order conditions, was monitored in real time using a newly developed laser-photofragment/laser-induced fluorescence technique (Carl, S. A.; Sun, Q.; Peeters, J. J. Chem. Phys. 2000, 114, 10332) that involved pulsed-laser photodissociation of HCCO at 266 nm and laser-induced fluorescence at ca. 430 nm of the resulting nascent rotationally excited CH(X 2 Π) photofragment. The rate coefficient of the title reaction was found to exhibit a negative temperature dependence described by k 5 (T) (HCCO+NO) ) (1.6 ( 0.2) × 10 -11 exp(340 ( 30 K/T) cm 3 s -1 molecule -1 (2σ errors). In combination with the recent theoretically determined branching ratios for this reaction of this laboratory (Vereecken, L.; Sumathy, R.; Carl, S. A.; Peeters, J. Chem. Phys. Lett. 2001, 344, 400), the temperature dependencies of the two dominant product channels, HCN + CO 2 and HCNO + CO, may be described by k 5a ) (3.7 ( 0.3) × 10 -10 T -0.72(0.02 exp(200 ( 30 K/T) cm 3 s -1 molecule -1 and k 5b ) (1.4 ( 0.2) × 10 -11 exp(320 ( 30 K/T) cm 3 s -1 molecule -1 , respectively, where the given (2σ) error limits are derived from those of the present experimental work only.

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Thermal oxidation characteristics of chemical vapor deposited (CVD) diamond films prepared by the hot filament method along with (111) and (100) oriented type II a natural diamond wafers were investigated in flowing oxygen at atmospheric pressure and in the temperature range 973–1173 K by thermogravimetry. Partially oxidized samples were also analyzed by x‐ray diffraction, Raman spectroscopy, and electron microscopy. On oxidation, diamond films attached to the silicon wafer turned black, while free standing diamond films did not undergo any color change. Both x‐ray diffraction and Raman spectroscopy failed to identify the transformation of diamond to nondiamond carbon forms. Electron microscopy and thermogravimetry indicated that CVD films were least resistant to oxidation followed by (111) surface and (100) surface of natural diamond. The oxidation rates of the CVD films which were dominated by (111) faces are close to those of (111) oriented natural diamond wafers. The apparent activation energies for the oxidation of the films, (111) and (100) oriented wafers are 229, 260, and 199 kJ/mole, respectively, suggesting that the films and the wafers oxidize by direct reaction between diamond and oxygen to CO and CO2 .

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