Ion/induced dipole

N2 - NO+ + N, compared with a theory (7) based on classical trajectories subject to an ion-induced dipole potential. The assumptions involved in calculating the measured cross-sections are noted in the text... 

Pulsed source techniques have been used to study thermal energy ion-molecule reactions. For most of the proton and H atom transfer reactions studied k thermal) /k 10.5 volts /cm.) is approximately unity in apparent agreement with predictions from the simple ion-induced dipole model. However, the rate constants calculated on this basis are considerably higher than the experimental rate constants indicating reaction channels other than the atom transfer process. Thus, in some cases at least, the relationship of k thermal) to k 10.5 volts/cm.) may be determined by the variation of the relative importance of the atom transfer process with ion energy rather than by the interaction potential between the ion and the neutral. For most of the condensation ion-molecule reactions studied k thermal) is considerably greater than k 10.5 volts/cm.). 

For ion-molecule reactions where the interaction can be attributed to ion-induced dipole forces it has been shown (11) that the rate constant should be independent of ion energy—i.e., the thermal and 10.5 volt cm.-1 rate constants should be the same. The third column in Table II shows that for most of the reactions studied the ratio k (thermal)/ (10.5 volts/ cm.) is in the range 0.7-1.1. Considering the errors involved this is not significantly different from unity, indicating that most of the reactions... 

In Table III we compare for several reactions the experimental rate constants with rate constants calculated on the basis of ion-induced dipole interactions only from the relation (4) ... 

The results in Table IV suggest that the condensation reactions cannot be described adequately by the ion-induced dipole model. In this regard the results agree with conventional studies which have frequently found a higher power inverse dependence of the cross-section on the field strength E for condensation reactions than for hydrogen transfer reactions. 

The first two terms C/cou and C/poL correspond to the empirical energy of ion-dipole and ion-induced dipole interactions, being given by... 

Because T -> V energy transfer does not lead to complex formation and complexes are only formed by unoriented collisions, the Cl" + CH3C1 -4 Cl"—CH3C1 association rate constant calculated from the trajectories is less than that given by an ion-molecule capture model. This is shown in Table 8, where the trajectory association rate constant is compared with the predictions of various capture models.9 The microcanonical variational transition state theory (pCVTST) rate constants calculated for PES1, with the transitional modes treated as harmonic oscillators (ho) are nearly the same as the statistical adiabatic channel model (SACM),13 pCVTST,40 and trajectory capture14 rate constants based on the ion-di-pole/ion-induced dipole potential,... 

As shown in Table 3.28, the to-bond energies typically fall within the range 30-50 kcal mol-1, somewhat weaker than corresponding 2c/2e bond energies (except for F2), but far stronger than noncovalent ion-dipole (or ion-induced-dipole)... 

Ion-Induced Dipole and Dipole-Induced Dipole Intermolecular Forces... 

For each of the substances the possible answers are ionic bonding, covalent bonding, metallic bonding, hydrogen bonding, dipole-dipole force, or London force. Forces, such as ion-dipole forces and ion-induced dipole forces, are not choices because these require the presence of two or more substances. For example, sodium chloride cannot utilize either of these two forces, but sodium chloride in water can. (Sodium chloride in water exhibits ion-dipole forces.)... 

Ion-induced dipole intermolecular forces occur between an ion and a nonpolar molecule. 

Because the collisions between ions and molecules in the gas phase are governed by physical (ion-dipole, ion-induced dipole) rather than chemical forces, it is possible to calculate rather accurately the collision rate constant (6, 7). We then express the efficiency of the reaction as the fraction of collisions which lead to products. 

An ion-induced dipole force results when an ion in close proximity to a non-polar molecule distorts the electron density of the non-polar molecule. The molecule then becomes momentarily polarized, and the two species are attracted to each other. This force is active during every moment of your life, in the bonding between non-polar O2 molecules and the Fe " ion in hemoglobin. Ion-induced dipole forces, therefore, are part of the process that transports vital oxygen throughout your body. 

A dipole-induced dipole force is similar to that of an ion-induced dipole force. In this case, however, the charge on a polar molecule is responsible for inducing the charge on the non-polar molecule. Non-polar gases such as oxygen and nitrogen dissolve, sparingly, in water because of dipole-induced dipole forces. 

---