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Following the arrival of Cassini at Titan in 2004, the Titan atmosphere has been shown to contain large complex polycyclic-aromatic hydrocarbons. Since Cassini has provided a great deal of data, there exists a need for kinetic rate data to help with modeling this atmosphere. One type of kinetic data needed is electron-ion dissociative recombination (e-IDR) rate constants. These data are not readily available for larger compounds, such as naphthalene, or oxygen containing compounds, such as 1,4 dioxane or furan. Here, the rate constants for naphthalene, 1,4 dioxane, and furan have been measured and their temperature dependencies are determined when possible, using the University of Georgia's Variable Temperature Flowing Afterglow. The rate constants are compared with those previously published for other compounds; these show trends which illustrate the effects which multirings and oxygen heteroatoms substitutions have upon e-IDR rate constants. [ABSTRACT FROM AUTHOR]

The flowing afterglow/Langmuir probe (FALP) technique has been extended to enable the neutral products of electron–ion dissociative recombination in thermalized afterglows to be identified by spectroscopic methods. Absolute number densities of H atoms in the afterglow have been determined using vacuum ultraviolet (VUV) absorption at the Lα wavelength. By exploiting the reaction H+NO2→OH+NO, all of the H atoms can be incorporated into OH molecules and thus observation of the intensity of laser induced fluorescence (LIF) If, obtained by exciting the (1,0) band of OH(A 2Σ←X 2Π), allows a calibration to be obtained of If against the known number density of OH X 2Π(ν‘=0) in the afterglow. Following this procedure, a recombining HCO+2 /electron afterglow was probed for production of ground state OH X 2Π(ν‘=0) using LIF and it was established that OH(ν‘=0) resulted from 17% of the recombining ground state HCO+2 ions. It was also established that a further 17% of the recombinations resulted in OH(ν‘>0), i.e., that, in total, (34±6)% of the HCO+2 ions recombine to produce OH X 2Π radicals, either directly or via the electronically excited A 2Σ state. Details of the calibration procedure for H and OH number densities, of the ion chemistry involved in the production of the HCO+2 afterglow plasmas and of the checks carried out to establish that the fluorescence observed was from OH produced in the recombination reaction are presented. During these experiments, the rate coefficient at 300 K for the H+NO2 reaction was determined to be 1.3×10-10 cm3 s-1 from observations of the H-atom decay as a function of NO2 number density in the afterglow (in good agreement with previous determinations). Also the rate coefficient for the quenching reaction of OH(ν‘>0) with NO to produce OH(ν‘=0) was determined to be 6×10-11 cm3 s-1. [ABSTRACT FROM AUTHOR]

Using the flowing afterglow/Langmuir probe (FALP) technique, we have determined (at variously 300 and 570 K) the dissociative attachment coefficients β for the reactions of electrons with the common acids HNO3 (producing NO-2) and H2SO4 (HSO-4), the superacids FSO3H (FSO-3), CF3SO3H (CF3SO-3), ClSO3H (ClSO-3,Cl-), the acid anhydride (CF3SO2)2O (CF3SO-3), and the halogen halides HBr (Br-) and HI (I-). The anions formed in the reactions are those given in the parentheses. The reactions with HF and HCl were investigated, but did not occur at a measurable rate since they are very endothermic. Dissociative attachment is rapid for the common acids, the superacids, and the anhydride, the measured β being appreciable fractions of the theoretical maximum β for such reactions, βmax. The HI reaction is very fast ( β∼βmax) but the HBr reaction occurs much more slowly because it is significantly endothermic. The data indicate that the extreme acidity of the (Bronsted-type) superacids has its equivalence in the very efficient gas-phase dissociative attachment which these species undergo when reacting with free electrons. The anions of the superacids generated in these reactions, notably FSO-3 and CF3SO-3, are very stable (unreactive) implying exceptionally large electron affinities for the FSO3 and CF3SO3 radicals. [ABSTRACT FROM AUTHOR]

The reactions of ions in the series PH+n (n=0 to 4) have been studied at 300 K with CH3NH2, PH3, NH3, CH3CCH, H2S, C2H4, CH3OH, COS, C2H2, O2, H2O, CH4, HCN, CO2, CO, and H2 using a selected ion flow tube (SIFT) apparatus. The majority are fast binary reactions, the measured rate coefficients, k, being close to the respective collisional values, and for reactions involving polyatomic reactant molecules multiple product ions are observed. Most reaction mechanisms are represented in this large number of reactions including charge transfer, proton transfer, atom abstraction and especially evident is phosphorus atom insertion in which product ions such as HnPN+, HnPO+, HnPS+ and HnCmP+ are formed. The reactions of the PH+n ions (n=0 to 2) with CO2, CO, and H2 proceed by the process of ternary association except for the P+ reaction with CO2, in which PO+ is formed in a fast binary reaction. PH+4 reacts only with CH3NH2 and NH3 by fast proton transfer, a process which is always rapid when it is exothermic. Upper limits to the heats of formation of HPO+, H2PO+, PC2H2+ and HCP have also been deduced from their observation as products of some of the reactions. [ABSTRACT FROM AUTHOR]