The different equilibria in HF and HF/HCI solutions are examined and the etching reaction of SiQ is investigated as a function of the different species present in the HF solution. A new model for the etching mechanism of SiO~ is developed based on the existence of the dimer of HF, (HF)~.The dissolution of SiQ in HF solutions is a fundamental step in the fabrication of integrated circuits. Mat and Looney ~ have studied the etch rate of SiO2 in HF solutions as a function of the concentration, the temperature, the oxide growth process, and the stirring of the solution. The overall chemical reaction involved is normally understood as

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The reaction of ethyne with atomic oxygen was investigated in the temperature range 300-600 K, at a pressure of 2 torr. With molecular beam mass spectrometry, both methylene and the ketyl radical were shown to be important primary products. An absolute measurement was made of the rate constant of reaction 7 of HCCO with O at T = 535 K: k1 = (1.10 ± 0.10) X 1014 cm1 23 mol"1 s"1. The activation energy was found to be £? = 0.6 ± 0.3 kcal mol"1. Reaction 2 of HCCO with H atoms is even faster; in Stern-Volmer experiments the ratio k^/k7 was determined to be 1.4 ± 0.

Publication costs assisted by the Nationaal Foods voor Wetenschappelijk Onderzoek Belgium Molecular beam sampling and subsequent mass spectrometric analysis have been used as detection techniques for methylene radicals produced in the oxidation process of acetylene with oxygen atoms in a fast flow reactor. Reactions of CH2 with oxygen atoms, molecular oxygen, and nitric oxide are investigated in the temperature region between 295 and 600 K. For reaction 2, CH2 + O, an activation energy of about 0 kcal mol™1 has been found while for reaction 3, CH2 + 02, the value Es = 1.5•± 0.3 kcal mol™1 is derived. Reaction 4, CH2 + NO, shows non-Arrhenius behavior and has a negative activation energy, £4 = -1.1 ± 0.4 kcal mol™1. In addition, complete Arrhenius expressions for the rate constants of reactions 3 and 4 are given and an attempt is made to determine the possible reaction products of these reactions.

Results of ab initio calculations comparing the 1,3-cycloadditions of ozone to ethylene, benzene, and phenol are presented. The potential energy surfaces of these reactions are explored to establish structures and relative energies of transition states and addition products. Calculations are performed at the B3LYP level for geometry optimizations and at the CCSD(T)/6-31G(d,p) level for energetics. For the ethylene reaction the calculated activation barrier and exothermicity correspond within a few kilocalories per mole with previous theoretical studies and experimental data, rendering credit to the computational model used. Calculations for the benzene ozonolysis yield a barrier of 15.8 kcal/mol that corresponds quite well with the experimental value of 14.6 kcal/mol. The phenol reaction is predicted to possess a barrier of 9.5 kcal/mol. The most stable primary ozonides of benzene and phenol are calculated at 18.9 and 29.0 kcal/mol below the corresponding entrance channels, respectively. In the specific case of the phenol ozonide, the most stable conformation for this intermediate is compatible with the experimentally determined initial reaction product catechol. The carbon rings in the primary ozonides of benzene and phenol are found to retain their planarity.