No abstract

While only one component was required to simulate the data, more than one product may have been involved, in which case the one component must be viewed as a surrogate having an effective SVP of 0.01 ppb or less. Adding trace amounts of SO2 greatly increased the nucleation rate while having negligible effect on the overall aerosol yield. We are unable to explain the observed nucleation in the a-pinene/ozone system in terms of classical nucleation theory. The nucleation rate and, more importantly, the slope of the nucleation rate versus the vapor pressure of the nucleating species would suggest that the nucleation rate in the c•-pinene/ozone system may be limited by the initial nucleation steps (i.e., dimer, trimer, or adduct formation).

No abstract

The gas-phase kinetics are reported for the reactions V(a4F3/,) + OX, where X = 0, N, and CO, in the temperature range 297-643 K. V atoms were produced by the multiphoton dissociation of VC14(g) at 193 nm and were detected by laser-induced fluorescence. Arrhenius rate expressions obtained for these reactions are k(Oz) = (1.20 f 0.26) X exp[-(2.16 f 0.19 kcal/mol)/RT] cm3 s-I, k(N0) = (2.20 f 0.26) X 10-l' exp[-(0.40 f 0.19 kcal/mol)/RT] cm3 s-I, and k(COz) = (4.38 f 0.62) X lo-" exp[-(2.90 f 0.14 kcal/mol)/RT]cm's-'. Also, room temperature rate constants were measured for the disappearance of the excited state V(a6D3/2) due to collisions with OX, Ar, and N2; the V* disappearance rates induced by collisions with the oxidants are found to be considerably faster than those of the ground-state atom, with rate constants (in units of cm3 s-I) k(Oz) = (1.34 f 0.21) X k(C02) = (2.17 f 0.35) X 10-l'. k(Ar) = (2.06 f 0.32) X Quoted uncertainities are f2a. The rates of collisional quenching are compared to the reaction rates of ground-state vanadium, and quenching mechanisms are discussed. k(N0) = (1.00 f 0.16) X and k(Nz) = (5.62 f 0.83) X

The fluorescence decay of NO3 excited to vibronic levels between the origin at 661.9 and ∼606 nm is measured and found to be nonexponential. An exponential fit to the long-lived portion of the decay gives an apparent, collision-free lifetime of 340±20 μs. Electronic quenching rates have been measured for a variety of collision partners including He, N2, O2, C3H8, and HNO3. Our results are interpreted in terms of the Douglas effect, i.e., an extensive coupling of excited electronic levels with nonemissive vibronic levels of the ground electronic state. This coupling is likely responsible for the anomalously long lifetime and the apparent diffuseness of the absorption spectrum.