title: Mass spectrometric study of three-body ion-molecule clustering reactions of CpHq+ ions with N2 or CH4 in N2-CH4 mixtures.
abstract: Thermochemical data for several ion-molecule clustering of hydrocarbon ions with N2 or CH4 were obtained from clustering equilibria studies in gas mixtures irradiated by alpha-particles.  High-pressure mass spectrometry was used to determine the enthalpy and entropy changes of clustering (delta H0 and delta S0, respectively) for the reactions X+(N2)n-1 + 2N2 <==> X(+)(N2)n + N2 with X = CH5, n = 1-2; X = C2H5, n = 1-4; and X = C3H7, n = 1.  For X = CH5, the values (delta H0; delta S0) are found to be (-6.8 kcal mol-1; -19.7 cal mol-1 K-1) for n = 1, and (-5.3 kcal mol-1; -15.9 cal mol-1 K-1) for n = 2.  For X = C2H5, (delta H0; delta S0) = (-6.9 kcal mol-1; -18.2 cal mol-1 K-1), for n = 1, and (-4.6 kcal mol-1; -20.8 cal mol-1 K-1) for n = 2.  From the equilibrium measurements at 129 K, estimates of the thermochemical values could be obtained for n = 3-4.  The results obtained for the free energy, delta G0, were -1.4 kcal mol-1 for n = 3, and -1.1 kcal mol-1 for n = 4.  For X = C3H7 we found delta G0 = -0.7 kcal mol-1 at 213 K.  The association reactions X+ + 2CH4 <==> X+(CH4) + CH4 with X = CH5, C2H5, C2H7, and C3H7 were also studied, resulting in free energy values at 206 K of -3.1, -1.9, -0.5 and -1.3 kcal mol-1, respectively.  The results for CH5, C2H5 and C3H7 are compared with previously reported measurements.
authors.affiliation: Departamento de Física, Universidade Federal de Santa Catarina, Florianópolis-SC, Brazil.
authors.forename: C V
authors.initials: CV
authors.lastname: Speller
authors.forename: J R
authors.initials: JR
authors.lastname: Vacher
authors.forename: E
authors.initials: E
authors.lastname: Duc
authors.forename: M
authors.initials: M
authors.lastname: Fitaire
mesh_terms: D001272:Atmosphere; D055598:Chemical Phenomena; D002621:Chemistry; D018559:Exobiology; D005118:Extraterrestrial Environment; D006838:Hydrocarbons / Q000032:analysis* / Q000737:chemistry; D007477:Ions; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods; D008697:Methane / Q000032:analysis* / Q000737:chemistry; D008956:Models, Chemical; D009584:Nitrogen / Q000032:analysis* / Q000737:chemistry; D018539:Saturn; D013696:Temperature; D013816:Thermodynamics
chemical_list: D006838:Hydrocarbons; D007477:Ions; D009584:Nitrogen; D008697:Methane