A modification of the conventional classical theory of vibrational–translational energy exchange is made which leads to an expression of increased accuracy and which has the proper behavior at high energy. It is pointed out that the refined impulse approximation can be used to calculate the energy transferred to an anharmonic oscillator in configurations where the potential energy curve has positive curvature. The case in which the oscillator potential has negative curvature is analyzed and is shown to lead to energy exchanges which exceed the predictions of the impulse approximation. Expressions are given for the energy transferred in grazing collisions which can be used to estimate total inelastic cross sections.

The absolute proton affinity of NH3 (203.6±1.3 kcal/mole at 298 K) and the proton solvation energies by more than one NH3 have been determined by the molecular beam–photoionization method. In addition, the NH3+–NH3 interaction energy (0.79±0.05 eV) has been measured by photoionization of the neutral van der Waals dimer. These experiments have shown that photoionization of van der Waals clusters is a very powerful method for determining the energetics of gas phase proton solvation.

The photoionization efficiency curve of the nitric oxide dimer (N0) 2 was obtained in the wavelength range from 1420$. to 1230~ (8.731 eV-10.080 eV). The ionization potential of (N0) 2 was found to be 8.752 eV ± 0.008 eV. From the structure of the photoion yield 2 + 1 +. curve of (N0) 2 , NO(II, V 11 =0)-NO (X E , v') 1s found to be bound when NO+(X 1 E+) is in the v'=O or 1 vibrational state. From this and the dissociation energy of (N0) 2 (0.069 eV ± 0~003 eV) obtained by• Billingsley and Callear, the dissociation energy of N0(2 rr, V 11 =0)-NO+(X1E+, v'=O) is deduced to be 0~57j eV ± 0.008 eV .