ALBERT

Beschreibung: We present an 11" resolution map of the central 2 pc of the Galaxy in the CO J = 7 --〉 6 rotational transition. The CO emission shows rotation about Sgr A* but also evidence for noncircular turbulent motion and a clumpy morphology. We combine our data set with available CO measurements to model the physical conditions in the disk. We find that the molecular gas in the region is both warm and dense, with T approx. 200-300 K and n(sub H2) approx. (5-7) x 10(exp 4) cm(exp -3). The mass of warm molecular gas we measure in the central 2 pc is at least 2000 M(solar), about 20 times the UV-excited atomic gas mass, ruling out a UV heating scenario for the molecular material. We compare the available spectral tracers with theoretical models and conclude that molecular gas is heated with magnetohydrodynamic shocks with v approx. 10-20 km s(exp -1) and B approx. 0.3- 0.5 mG. Using the conditions derived with the CO analysis, we include the other important coolants, neutral oxygen and molecular hydrogen, to estimate the total cooling budget of the molecular material. We derive a mass-to-luminosity ratio of approx. 2-3 M(solar)(L(solar)exp -1), which is consistent with the total power dissipated via turbulent decay in 0.1 pc cells with v(sub rms) approx. 15 kilometers per second. These size and velocity scales are comparable to the observed clumping scale and the velocity dispersion. At this rate, the material near Sgr A* is dissipating its orbital energy on an orbital timescale and cannot last for more than a few orbits. Our conclusions support a scenario in which the features near Sgr A* such as the circumnuclear disk and northern arm are generated by infalling clouds with low specific angular momentum.

Beschreibung: Results are reported for an experimental study of the reactions of O(1D) with CCl4, CFCl3, CF2Cl2, CHFCl2, CHF2Cl, and CF2ClCFCl2 over the temperature range from 173 to 343 K, based on the time-resolved emission of O(1D) at 630 nm. The experiments involved photolysis of O3 by Nd-YAG laser pulses and measurements of 630-nm emission intensity in mixtures with He and the various halocarbons. Pseudo-first-order rate constants are derived from plots of the logarithms of the 630-nm emission intensities as a function of time for particular He/O3/halocarbon mixtures, and second-order rate constants are then obtained from plots of these pseudo-first-order rate constants as a function of halocarbon concentration at constant He and O3 concentrations. No temperature dependence of the second-order rate constants is observed over the range studied, within the precision of the measurements. It is found that the rate constants decrease as H is substituted for Cl in a halocarbon molecule and as F is substituted for H or Cl.

Beschreibung: Rate constants for the quenching of O2(1-Sigma sub g(+)) in the temperature range 170-400 K were obtained by observing the change in the rate of decay of this oxygen emission as a function of HBr concentration. At each temperature the decay was observed at eight different HBr concentrations ranging from 0 to 6 x 10 to the -6th moles/l. It is found that long range multipolar interactions make a major contribution to the quenching of the oxygen molecule by H2, with the quenching shown to be most effective at low temperatures. Short range repulsive interactions may also contribute to the quenching process, especially at high temperatures. The suggestion that the quenching process is dominated by the ability of the quencher to take up the energy of the oxygen molecule transition in vibrational and rotational motion is confirmed.

Beschreibung: Absolute rate constants for the deactivation of O(1D) atoms by some atmospheric gases have been determined by observing the time-resolved emission of O(1D) at 630 nm. O(1D) atoms were produced by the dissociation of ozone via repetitive laser pulses at 266 nm. Absolute rate constants for the relaxation of O(1D) at 298 K are reported for N2, O2, CO2, O3, H2, D2, CH4, HCl, NH3, H2O, N2O, and Ne. The results obtained are compared with previous relative and absolute measurements reported in the literature.

Beschreibung: Absolute rate constants for the deactivation of O(1D) by CO have been measured at temperatures between 113 and 333 K. A very small temperature dependence is observed and is described by the Arrhenius expression (4.7 + or - 0.9) times 10 to the -11th power exp(126 + or 33)/RT cu cm/molecule-sec, where E is in cal/mol.

Beschreibung: The rate constants for the deactivation of O(1D) by Xe, Kr, and Ar were measured over the range 110-330 K. Only Xe had a significant temperature dependence. Its Arrhenius expression is (8.5 + or - 1.7) times 10 to the -11th power exp(-103 + or - 52)/RT cu cm/molecule-sec. The rate constants for Kr and Ar are (6.4 + or - 1.3) times 10 to the -12th power and (5.0 + or - 1.5) times 10 to the -13th power cu cm/molecule-sec, respectively. The observed trend in deactivation efficiency, Xe (greatest), Kr, Ar (least), and the observed temperature effects support the results and the spin-orbit interaction mechanism for deactivation given by Husain and co-workers.