M.A.D. Fluendy

Spectroscopy and dynamics of nitromethane (CH3NO2) and its anionic states

Abstract Dissociative electron attachment in nitromethane has been investigated along with related spectroscopic measurements made using optical and electron scattering methods. The nature and dissociation dynamics of the low-lying anionic states of nitromethane are discussed in the light of these experiments and the results of ab initio molecular orbital computations.

Elastic scattering of alkali atoms from iodine atoms and molecules at thermal energies

High-resolution, small-angle measurements of the elastic differential cross sections have been made for the systems K/I and K/I2. In all cases the structure at small angles is found to arise predominantly from collisions occurring along the adiabatic potential. The off-diagonal matrix element of the electronic hamiltonian between the covalent and ionic states in the K/I system is found to be ∼ 6×10-15 ergs.

Classical trajectory studies of the collision system K+I2 in the eV region

Abstract Trajectory calculations on the lowest adiabatic surface for K+I 2 have been used to explore reactive and inelastic scattering in the eV region. These processes are found to proceed by two contrasting mechanisms, one using the attractive parts of the potential and the other the repulsive wall. The probability of processes occurring through attractive forces decreases with increasing collision energy while the short range mechanism is essentially a two body one with three body effects only making a contribution in a limited impact parameter range. A hard sphere spectator model is explored, but found to be quite inadequate for energy loss calculations. A spectator model with realistic interatomic forces is, in contrast, successful in interpeting the whole range of numerical results above about 20 eV. It is suggested that a two body potential will be useful in interpreting even very inelastic high energy scattering provided that the mass ratio is favourable.

Energy partitioning in the reaction F + I2

Abstract The vibrational populations and rotational temperature of the IF product formed in the reaction F + I 2 → IF + I have been measured using a crossed-beam laser-induced fluorescence technique. The relative collision energy was 90 meV. Measurements of the relative populations in the υ = 0, 1 and 2 levels showed a strong population inversion with an effective temperature of −3000 K, corresponding to a fraction of the total energy, f υ > = 0.6 ± 0.1, appearing in product IF vibration. In contrast, the product was rotationally cold with f R > ≈ 0.02. The results are consistent with a direct dynamical process for this reaction.

Atomic scattering from heavy P-state atoms. Role of depolarization

The anisotropy of the potential between two atoms, one at least of which has J > ½, can cause partial re-alignment of the electronic angular momentum vector (i.e. MJ transitions) during collision. Within the framework of the semi-classical approximation, a single parameter akin to the Massey parameter is found to determine whether a given system will exhibit strong or weak coupling of the electronic to the relative atomic angular momentum. The consequence of these two coupling schemes for the position of the rainbow, the quenching of glory undulations and the magnitude of the total cross section are discussed. Particular reference is made to the metastable 3 P 2 state of Hg and the inert gases where the fine structure splitting is much larger than the relevant part of the interatomic potential. In the case of Kr* and Xe* the rainbow and glory features are strongly dependent on the initial MJ state of the atom and the glory structure should be suppressed. In contrast, scattering from systems such as Hg*/Na...

Non-adiabatic processes in alkali metal-alkyl halide molecule collisions

The mechanism for vibronic excitation and ion pair production in alkali metal-alkyl halide collisions is investigated. A classical trajectory surface hopping model is developed to account for the fourteen exit channels for which data is available. It is shown that the ground ionic intermediate accounts for the observed A state excitation in CH3I as well as the production of excited alkali atoms. It is further shown that the other, more highly excited, processes can be understood on the basis of an electron harpoon to form one of a sequence of strongly ionic doorway states. Each doorway state connecting to a manifold of exit channels. The nature of these doorway states and the role of vacancy production in their excitation is discussed.

Electron transfer in alkali atom CH3NO2 collisions

Vibrational and electronic excitations in alkali metal atom-nitromethane collisions at relative energies of 40–160 eV have been observed. The inelastic processes observed are similar to those seen in the analogous alkyl halide systems and are interpreted via a similar sequential electron capture and recapture mechanism. The dynamics are determined by the molecular orbital into which capture occurs with the excited state corresponding to capture into the σ* orbital rather than the lowest unoccupied orbital (π*) dominating the dynamics.

Electronic excitation in potentially reactive atom–molecule collisions

Inelastic differential scattering cross sections for the system potassium + alkyl halide have been measured in the small angle region for Eχ between 20–1000 eV°. Electronic excitation of both collision partners is seen together with vibrational excitation of the alkyl halide.Evidence is adduced suggesting that excitation occurs by either of two paths corresponding to the preliminary transfer of an electron in the entrance channel or as the colliding pair recedes. A harpooning model incorporating bond stretching in the negative molecular ion is developed that agrees well with most of the observations.

Electronic excitation andd energy transfer in K-N2 collisions

Abstract Inelastic differential scattering cross sections for the system K/N 2 have been measured in the small-angle regime for E x in the range 80–600 eV deg. A cross beam time-of-flight technique was used to measure energy transfer effects occurring in the collision. The dominant inelastic process in the region explored was production ot the K(4 2 P) state together with simultaneous vibrational excitation of the N 2 molecule. The observations are in excellent agreement with published potentials and a simple classical model involving an intermediate with considerable negative-ion character.

Electronic excitation in potassium/alkyl halide collisions—The electron harpoon

Inelastic differential scattering cross sections for collisions between potassium atoms and CH3I, C3H7I, CH3Cl, CF3I and HI are reported for the reduced scattering angle range from 20–1000 eV°. The measurements were made in the quasi-rectilinear trajectory regime using a velocity change method. Electronic excitation of the K atom accompanied by substantial vibronic excitation of the target molecule extending to the lower Rydberg states is seen in all the systems studied. The results are in accord with an electron harpoon model involving successive donation and recapture of an electron by the potassium atom. In the case of collisions leading to the ground electronic state of the molecule a doorway state similar, but not identical, to the molecular negative ion is involved and a model incorporating the effects of bond stretching—analogous to that advanced to interpret collision induced ionization in alkali metal + halogen molecule collisions—is in excellent agreement with the observations. Excited electroni...