Vibrationally state - selected reactions of ammonia ions . I . NH 3 + ( v ) + O 2 Richard

ion in the NH3+ IH20 system. 34 The D2 molecule can interact directly with the electron density on the nitrogen in this configuration. Other configurations such as the above but with the D2 rotated by 90· or an in-plane approach appear less favorable. Ab initio and semiempirical calculations of portions of the NH/ potential energy surface indicate that the above configuration represents a minimum energy approach and that the system must overcome a small barrier to form the highly stable NH3D+ ---D complex. 35-37 Vibration in the V 2 umbrella-bending mode is directed along the reaction coordinate in such a transition state. Increased vibration in this mode deforms the system towards the geometry of the tetrahedral product, which might suggest an increase in the total reaction cross section, but the experimental results show that the total reaction cross section is roughly independent of the V2 excitation. Whether steric hindrance from the hydrogens on the ammonia, the small mass of the spectator partner, or some other factor account for this behavior is presently a matter of conjecture.