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'Carbon' formation, in the temperature range 600-1200 K, by thermal decomposition of sulphanilic acid has been studied using electron spin resonance and X-ray photoelectron spectroscopy supported by chemical investigations. Evidence is put forward which suggests that these 'carbons' are a class of disordered free radical solids formed by cross-linking of tetra-azadibenzanthracene structural units and also containing heterocyclic sulphur.

Non-adiabatic quasi-classical trajectories have been carried out on the B˜-X˜1A' two-valued surface of H2O using initial conditions which are appropriate to photodissociation via the B˜state. Two models have been used. One of these involves surface hopping between adiabatic surfaces and the other integrates the electronic density matrix in a diabatic basis along a classical trajectory. The results of the two are in broad agreement. The majority of OH fragments are formed in the OH(2Π) state which is consistent with experimental findings. Approximately 10 per cent of trajectories lead to O(1D) + H2. The majority of OH(2Σ+) is produced in high rotational states of v = 0, which is also confirmed by experiment. However, the calculations predict large populations of high vibrational states of OH(2Π) which disagrees with experiment. For this reason it is likely that OH(2Π) is mainly produced by the alternative B˜-Ã non-adiabatic process.

Quasi-classical trajectories have been carried out on a 2-valued surface for the singlet ground state of H2O. The calculated rate constants for both O(1D) + H2(1Σg+) →OH(2Π) + H(2S) and D(2S) + OH(2Π) →H(2S) + OD(2Π) are in good agreement with experimental values. For D(2S) + OH(2Π) collisions above 2 eV, O(1D) can be produced but the probability for this is low.

State-to-state transition probabilities have been calculated for collinear collisions of the type[image omitted]for a range of collision energies and small and large values of a non-adiabatic coupling parameter. Comparison has been made between the results of quantum mechanical coupled channel calculations, and two trajectory based models; a surface hopping and a modified classical path model. The quantum mechanical charge transfer probabilities show oscillations in the energy spectrum which we attribute to resonances in the reactant channel. Oscillations are also shown in the classical path calculations. The surface hopping charge transfer probabilities vary smoothly with collision energy, and at low energies the transition probabilities are much higher than the quantum mechanical results, particularly for low values of the non-adiabatic coupling parameter. The relative state-to-state transition probabilities (0-v'/0-0) are overestimated by both trajectory models; the Franck-Condon factors, in contrast, underestimate these factors. For v' ≥ 2 the classical path ratios are much better than either the surface hopping or Franck-Condon values.