Atomic‐Beam Scattering Studies on the Li☒Hg System: Quantum Effects and Velocity Dependence of the Cross Sections

Measurements of the velocity dependence of the angular intensity distribution of 6Li and 7Li beams scattered by a crossed Hg beam are reported. The Li beams were velocity selected, the Hg beam Maxwellian. Angular intensity distributions were measured at various relative velocities (vr) from 700–1200 m/sec, relative total cross sections (q) from vr=300 to 1350 m/sec. The differential cross sections show expected quantum interferences. Scattering patterns for 6Li— and 7Li☒Hg are found to be identical at the same de Broglie wavelength. The over‐all angular dependence of the scattering at low angles follows the θ−7/3 relationship characteristic of an r−6 long‐range potential. Extrema in the total cross sections q(vr) were also observed. The experimental data were analyzed in terms of a Lennard‐Jones (12, 6) potential, but it was not possible to determine a unique set of potential parameters. Comparison of observed and calculated results has yielded three nearly equivalent sets of σ, ϵ lying within the ranges 2.5≤σ≤3.5 Å, 480°≤ϵ/k≤1000°K.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69950/2/JCPSA6-42-7-2295-1.pd

Acquisition of regional air quality model validation data for nitrate, sulfate, ammonium ion and their precursors

An intensive field study was conducted throughout California's South Coast Air Basin to acquire air quality model validation data for use with aerosol nitrate formation models. Aerosol nitrate, sulfate, ammonium, other major ionic aerosol species, nitric acid gas and ammonia were measured concurrently at ten sites for forty-eight consecutive hours during the period 30–31 August 1982. Ozone, NO and NO_x were measured at all locations, and PAN was measured at Pasadena and Riverside, completing a nitrogen balance on the air masses studied. The product of the measured nitric acid and ammonia concentrations ranged from less than 1 ppbv^2 to greater than 300 ppbv^2 during the experiment, providing a wide range of conditions over which comparisons can be drawn between chemical equilibrium calculations and experimental results. The ionic material in the aerosol phase was chemically more complex than is assumed by present theoretical models for the equilibrium between NH_3, HNO_3 and the aerosol phase, and included significant amounts of Na^+, Ca^(2+), Mg^(2+), K^+ and Cl^− in addition to NH_4^+, SO_4^(2−) and NO_3^−. Results of the experiment showed that aerosol nitrate levels in excess of 20 μm^(−3) accumulated in near-coastal locations in the morning of 31 August, followed by subsequent transport across the air basin. Trajectory analysis showed that the afternoon aerosol nitrate peak observed inland at Rubidoux near Riverside was associated with the same air mass that contained the high morning nitrate levels near the coast, indicating that description of both transport and atmospheric chemical reactions is important in understanding regional nitrate dynamics

Bonding in Mercury-Alkali Molecules: Orbital-driven van der Waals Complexes

The bonding situation in mercury-alkali diatomics HgA (2Σ+) (A = Li, Na, K, Rb) has been investigated employing the relativistic all-electron method Normalized Elimination of the Small Component (NESC), CCSD(T), and augmented VTZ basis sets. Although Hg,A interactions are typical of van der Waals complexes, trends in calculated De values can be explained on the basis of a 3-electron 2-orbital model utilizing calculated ionization potentials and the De values of HgA+(1Σ+) diatomics. HgA molecules are identified as orbital-driven van der Waals complexes. The relevance of results for the understanding of the properties of liquid alkali metal amalgams is discussed

Real-time, in situ measurements of atmospheric optical absorption in the visible via photoacoustic spectroscopy--IV. Visibility degradation and aerosol optical properties in Los Angeles

Aerosol light absorption (babs) has been measured in real-time in Los Angeles with a validated photoacoustic technique, and its impact on visibility degradation has been examined. These measurements were collected during ten days in the summer of 1987 for the Southern California Air Quality Study (SCAQS). Aerosol babs ([lambda] = 514.5 nm) varied from an hourly average value of 7 x 10-6 m-1 in the 3-4 and 4-5 a.m. periods of 13 July to 9 x 10-5 m-1 in the 7-8 a.m. period of both 28 August and 3 September. This babs, which is due solely to elemental carbon (EC) showed a distinct diurnal pattern with low values at night, increasing around sunrise to higher values through mid-afternoon. Comparison of these data with aerosol light scattering data clearly illustrates that the contribution of aerosol light absorption to visibility degradation increases in importance under less polluted conditions. Other urban and rural studies show similar results.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28906/1/0000743.pd