Amorphous carbon films grown with fluorohydrocarbons can be grown to have dielectric constant values around 2.0. The behavior of these films when subjected to thermal excursion is studied. We have investigated material deposited in an ECR plasma, and find that the F:H ratio of the gas mixture is a good guide to material properties. Films deposited at 5°C were placed in a vacuum chamber at 400°C as long as 60 minutes. The film thickness, dielectric constant, and infrared absorption spectrum change with the F:H ratio of the incoming gas and thermal cycling. It was found that the dielectric constant and loss tangent decrease upon heating and that there is an apparent increase in C=C groups. As expected, as the F:H ratio increases, the dielectric constant and thermal stability decrease. Good thermal stability is shown for F:H ratios of 1.5, which result in films with a dielectric constant of ∼2.4 after heating.
The kinetics of the reaction BrO + N02 + M -* BrN03 + M were studied from ~1 to 700 torr at 298 K. The discharge-flow-mass-spectrometric (1-6 torr) and flash-photolysis-ultraviolet absorption (50-700 torr) techniques were used to monitor the pseudo-first-order decay of BrO (2 ) radicals in the presence of excess N02. The reaction was found to be in the third-order region from 1 to 6 torr and in the falloff region between secondand third-order kinetics in the 50-700-torr pressure range. Estimates of the limiting thirdand second-order rate constants, k0 and were determined by fitting the observed falloff curve (50-700 torr) to a theoretical expression developed by Troe and co-workers. The value of k0 derived by this method was in good agreement with the third-order rate constant determined in this study using the technique of discharge flow-mass spectrometry. Based on these two independent determinations, a value of (5.0 ± 1.0) x 10~31 cm6 molecule"2 s"1 is recommended for k0 ( = N2) at 298 K. The stratospheric implications of these measurements are discussed.
A photoionization mass spectrometric investigation of CH3CN and CD3CN from the onset of ionization to ∼20 eV is reported. Photoionization efficiency (PIE) curves of the acetonitrile parent ions and of the fragments C2H2N+, C2HN+, CH2N+, CH+3, CH+2 and their deuterated analogs have been measured. The parent ion curves display isotope-dependent direct ionization as well as autoionization structure. Excitation of one quantum of the doubly degenerate CCN bending mode (ν8) in the ground state of CH3CN+ is observed, indicating the presence of Jahn–Teller coupling. The measured ionization potentials are 12.194±0.005 eV (CH3CN) and 12.235±0.005 eV (CD3CN). Autoionizing Rydberg series converging to the first and second excited electronic states have been observed and assigned. At their thresholds, C2H2N+ and C2D2N+ are produced exclusively from parent ion states which are populated by autoionization. Appearance potentials of the fragment ions for which PIE curves were obtained are reported, and their heats of formation have been calculated where more reliable literature values are not available. The observed fragment ion appearance potentials and relative ion yields indicate that H-atom migrations in the molecular ion are important in the fragmentation mechanisms.
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