Ion-polar molecule collisions. Proton transfer reactions of H3+ and CH5+ to the geometric isomers of difluoroethylene, dichloroethylene, and difluorobenzene

Abstract

Proton transfer rate constants from CH5+, CD5+, H3+, and D3+ to difluoroethylene, dichloroethylene, and difluorobenzene isomers have been measured at thermal ion energies and compared with a classical theory of the ion-dipole interaction. Most experimental rate constants of nonpolar isomers are close to those predicted by the charge-induced dipole theory. Experimental and theoretical results for the polar isomers are also in good quantitative agreement. The effects of a permanent dipole on proton-transfer reactions are much less than predicted by the locked-dipole approximation, and the dipole effect increases with increasing µ / /'-ratio.Recent papers from this laboratory1•2 have reported . the charge-transfer reactions of rare gas ions with difluoroethylene, dichloroethylene, and difluorobenzene geometric isomers. It was shown that the effects of a permanent dipole on charge-transfer1•2 reactions are much smaller than expected by the "locked-dipole" approximation. The average dipole orientations are near tt/2 with respect to the line of collision. A classical theoretical model considering the thermal molecular rotational energy has been developed2 to estimate the capture cross-sections for ion-dipole reactions. The charge-transfer rate constants previously measured1•2 were considered to be composed of two components k = kcap + ke j(1) kcap corresponds to collisions occurring with impact parameters less than or equal to the capture limit. kej corresponds to collisions exceeding the capture limit where it is assumed the charge-transfer reaction takes place via a nonadiabatic electron jump.3•4 The theoretical predictions were in excellent agreement with experimental values of kcap. It was assumed that the long-range electron jump reactions show little dependence on the dipole moment.5 Here, we report a study of the proton-transfer reactions from CHS+, CD3+, H3+, and D3+ to the three sets of isomers mentioned above and compare the dipole effects with theoretical predictions. H3+ and CH5+ are easily accessible sources of protons that can readily be transferred to most gaseous molecules. Such transfers are often highly exothermic due to the low proton affinities of H26•7 and CH4.8 These reactions differ from the charge transfer reactions in that a massive particle is transferred rather than an electron and that the transferred particle originates on the impacting ion rather than the neutral molecule.(1) . T. Bowers and J. B. Laudenslager, J. Chem. Phys., 56, 4711 (1972).(2) T. Su and . T. Bowers, ibid., in press.(3) . T. Bowers and D. D. Elleman, Chem. Phys. Lett., 16, 486 (1972).(4) J. Gauglhofer and L. Kevan, ibid., 16, 492 (1972).(5) Theoretical calculations (ref 2) indicate that at collision diameters significantly larger than orbiting, virtually no orientation of the dipole occurs.

Gas‐Phase Studies of Formamidopyrimidine Glycosylase (Fpg) Substrates

“…[38,39] We therefore "back out" the neutral pressure from ac ontrol reaction (as described previously). [9,12,13,16,40,41]…”

The reaction of CF2Cl2 with gas-phase hydrated electrons

“…The measured experimental rate constants k abs are compared with the calculated collision rates to determine the reaction efficiency. We have shown previously that average dipole orientation (ADO) theory, [45][46][47][48] which describes the ion as a point charge, underestimates the collision rate of clusters with more than 10 water molecules (k ADO = 6.1 Â 10 À10 cm 3 s À1 for reaction with CF 2 Cl 2 ). We therefore use models that account for the geometric size of the water cluster, in particular the hard sphere average dipole orientation, k HSA = 1.0 Â 10 À9 cm 3 s À1 , and the surface charge capture model, k SCC = 2.0 Â 10 À9 cm 3 s À1 .…”

Formação e reatividade de íons negativos solvatados em fase gasosa por espectroscopia de ressonancia ciclotrônica de íons

“…O tamanho pequeno desta cela permite o uso de um de laboratório comercial cuja homogeneidade chega a uma pa em 10 A(W l ) = q E l /4m(w C -w l )< sen (wc-wl)t > Integrando-se o valor de A( 1) pelo tempo de re cia do 'íon na região analisadora:…”

“…A extensão desta teoria para ir o efeito do momento dipolar na colisão íon-molécula é satisfatoriamente pelo tratamento de Bowers e Su 9 o qual [10][11][12] uma boa comprovação experimental.…”

“…27 -29 Hoje em dia a ressonância ciclotrônica de ions técnica extremamente ver~átil e sensivel de detecção de Espectros de massa de média resolução de íons formados p pacto de elétrons podem ser obtidos a pressões da ordem Torr N.m-2 ); produtos de reações ion-molécula -6 ser observados acima de 10 Torr, devido ao longo tempo sj ência dos íons na cela.…”