Rate Constants and Cross Sections

Ion-Transport Catalysis: Catalyzed Isomerizations of NNH+ and NNCH3+

“…For example, HF, which has a relatively high dipole moment (2.0 D), forms an initial complex ( 9a ) that is stabilized by 35 kJ mol -1 , while H 2 with a zero dipole moment forms an initial complex ( 10a ) that is stabilized by only 3 kJ mol -1 . N 2 , which also has a zero dipole moment, forms a complex ( 11a ) that is stabilized by a greater amount (16 kJ mol -1 ) due to a combination of ion−induced-dipole and ion−quadrupole interactions . The magnitudes of both the polarizabilty and quadrupole moment of nitrogen are larger than those for hydrogen, resulting in the increased stabilization of the nitrogen complex.…”

Observation of a stripping threshold for the reaction N2++CH4→N2H++CH3

“…This internal energy distribution, in turn, will depend both upon the ionization conditions and upon the delay time between ion formation and reaction. 11 It is c~nceivable, for example, that N 2 H+ is formed predominantly by the reaction of N; in an electronically excited state (e. g., A 2rr u ), and that the apparent decrease in the reaction cross section is due to a decreased proportion of the excited state in the primary ion beam as the flight time from ion source to collision chamber exceeds the radiative lifetime for that excited state. However, the fact that similar threshold behavior was observed for the reaction of ground state Ar+ with CH 4 5b leads us to doubt internal excitation of the N; is the cause of the translational energy threshold observed for Reactions (2) and (3).…”

Effects of Internal Energy on Ion-Molecule Reactions

“…This behavior has been rationalized by a statistical phase space argument which has been discussed at length recently by . Henchman (1972) and can be described briefly as follows. If the reactants have no internal energy and very little kinetic energy and the reaction is strongly exothermic, the ratio of the volume in phase space available in the product channel to that in the (backward) reactant channel is very large and the forward reaction is strongly favored.…”

“…Schmeltekopf et al (1971) have found a very strong increase of the rate constant for the reaction 0 + (N 2 ,N)N0 + with increasing vibrational energy of Np. While the interpretation of the iaany unusual characteristics of this reaction is still a matter of some controversy (Henchman, 1972), the negative temperature dependence of the thermal rate constant from 80°K to 600°K and the positive effect of vibrational excitation suggest separate low and high energy mechanisms and in any case provide a rather stringent test of any proposed mechanism,, These latter two examples show how the effects of vibrational energy give important clues regarding reaction mechanism.…”

“…Such non-adiabatic processes can of course also be important in the case of reactants in electronic ground states since these need not even initially be on the lowest potential surface as for example the case of Ar + ( 2 P,-/p ground state) + Hg which at large distances lies above the surface for Ar + Hg + (v = o).'' Indeed two of the most thoroughly investigated reactions in which nonadiabatic processes are important involve ground stj^e reactants: H + (H2,H) H e + and O + (N 2 ,N) N0 + (Henchman, 1972).…”