Radiative Association Process Research Articles

An approach to the estimation of polyatomic vibrational radiative relaxation rates

A new method is presented for estimating spontaneous emission rates A(s −1) of polyatomic molecules in highly excited vibrational states. The method is used to calculate these rates as functions of vibrational energy for a variety of molecules. At vibrational energies of 1–5 eV, rates A of 10–10 3s −1 are calculated that increase with increasing vibrational energy and display a spread of an order of magnitude at each specific energy. For example, the HO 2 radical has A ≈ 100 s −1 at 1 eV and A ≈ 600 s −1 at 5 eV whereas C 2H 4 has A ≈ 15 s −1 at 1 eV and A ≈ 90 s −1 at 5 eV. If mechanical and electrical harmonicity are assumed, A is found to be linearly dependent on vibrational energy if this energy significantly exceeds the zero-point energy. The theory should prove useful in estimating rates of radiative Stabilization in radiative association processes.

Ion-molecule association

Radiative and ternary ion-molecule association are considered. The defects of the simple widely used model of these processes are discussed in detail and an improved version is given. The formulation involves V the ratio of the total partition function of the excited complex formed to the product of the total partition functions of the reactants. It is shown from RRKM theory that a good approximation V is inversely proportional to the product of the internal partition functions of the reactants so that its temperature dependence is well determined. This is also the temperature dependence of the radiative association process. The temperature dependence of the ternary association process in the low ambient gas density region is that of V beta where beta is a stabilisation efficiency factor. It is tentatively suggested that in this region beta may vary between as T-3/2 and as (T+ theta )-3/2 where T is the temperature and theta is a constant. At high densities beta is unity.