Penny Thorn

Cross sections and oscillator strengths for electron-impact excitation of the à 1B1 electronic state of water

The authors report absolute differential and integral cross section measurements for electron-impact excitation of the A (1)B(1) electronic state of water. This is an important channel for the production of the OH (X (2)Pi) radical, as well as for understanding the origin of the atmospheric Meinel [Astrophys. J. 111, 555 (1950)] bands. The incident energy range of our measurements is 20-200 eV, while the angular range of the differential cross section data is 3.5 degrees -90 degrees . This is the first time such data are reported in the literature and, where possible, comparison to existing theoretical work, and new scaled Born cross sections calculated as a part of the current study, is made. The scaled Born cross sections are in good agreement with the integral cross sections deduced from the experimental differential cross sections. In addition they report (experimental) generalized oscillator strength data at the incident energies of 100 and 200 eV. These data are used to derive a value for the optical oscillator strength which is found to be in excellent agreement with that from an earlier dipole (e,e) experiment and an earlier photoabsorption experiment.

A dynamical (e,2e) investigation of the structurally related cyclic ethers tetrahydrofuran, tetrahydropyran, and 1,4-dioxane

Triple differential cross section measurements for the electron-impact ionization of the highest occupied molecular orbitals of tetrahydropyran and 1,4-dioxane are presented. For each molecule, experimental measurements were performed using the (e,2e) technique in asymmetric coplanar kinematics with an incident electron energy of 250 eV and an ejected electron energy of 20 eV. With the scattered electrons being detected at -5°, the angular distributions of the ejected electrons in the binary and recoil regions were observed. These measurements are compared with calculations performed within the molecular 3-body distorted wave model. Here, reasonable agreement was observed between the theoretical model and the experimental measurements. These measurements are compared with results from a recent study on tetrahydrofuran [D. B. Jones, J. D. Builth-Williams, S. M. Bellm, L. Chiari, C. G. Ning, H. Chaluvadi, B. Lohmann, O. Ingolfsson, D. Madison, and M. J. Brunger, Chem. Phys. Lett. 572, 32 (2013)] in order to evaluate the influence of structure on the dynamics of the ionization process across this series of cyclic ethers.

Electron excitation and energy transfer rates for H2O in the upper atmosphere

Recent measurements of the cross sections for electronic state excitations in H2O have made it possible to calculate rates applicable to these excitation processes. We thus present here calculations of electron energy transfer rates for electronic and vibrational state excitations in H2O, as well as rates for excitation of some of these states by atmospheric thermal and auroral secondary electrons. The calculation of these latter rates is an important first step towards our aim of including water into a statistical equilibrium model of the atmosphere under auroral conditions.PACS Codes: 34.50.Gb 34.50.Ez

Cross sectons for the electron impact excitation of the a3B1, b3A1, B1A1 dissociative electronic states of water

Absolute differential and integral cross section measurements for electron impact excitation of the dissociative B1, A1 and A1 electronic states of water are described. These are very important channels for the production of OH (X2Π, ν) radicals, as well as for understanding the origin of the atmospheric Meinel bands. The energy range of our measurements is 20–50 eV, with the angular range of the differential cross section data being 10°–90°. Where possible comparison of the present cross sections with the corresponding results from theoretical calculations is made, the level of agreement between them being found to be quite marginal.

Application of the BEf-scaling approach to electron impact excitation of diople-allowed electronic states in molecules

We consider the efficacy of the BEf-scaling approach, in calculating reliable integral cross sections for electron impact excitation of dipole-allowed electronic states in molecules. We will demonstrate, using specific examples in H2, CO and H2O, that this relatively simple procedure can generate quite accurate integral cross sections which compare well with available experimental data. Finally, we will briefly consider the ramifications of this to atmospheric and other types of modelling studies.

Dynamical (e,2e) Investigations of Structurally Related Cyclic Ethers

Experimental and theoretical cross sections are presented for electron-impact ionization of a series of cyclic ethers.

Cross sections for the electron impact excitation of the \tilde{\rm a}^{3} B1, \skew{-3}\tilde{\rm b}^{3} A1 and \tilde{\rm B}^{1} A1 dissociative electronic states of water

Absolute differential and integral cross section measurements for electron impact excitation of the dissociative B1, A1 and A1 electronic states of water are described. These are very important channels for the production of OH (X2Π, ν) radicals, as well as for understanding the origin of the atmospheric Meinel bands. The energy range of our measurements is 20–50 eV, with the angular range of the differential cross section data being 10°–90°. Where possible comparison of the present cross sections with the corresponding results from theoretical calculations is made, the level of agreement between them being found to be quite marginal.

Cross sections for the electron impact excitation of the B1, A1and A1dissociative electronic states of water

Absolute differential and integral cross section measurements for electron impact excitation of the dissociative B1, A1 and A1 electronic states of water are described. These are very important channels for the production of OH (X2Π, ν) radicals, as well as for understanding the origin of the atmospheric Meinel bands. The energy range of our measurements is 20–50 eV, with the angular range of the differential cross section data being 10°–90°. Where possible comparison of the present cross sections with the corresponding results from theoretical calculations is made, the level of agreement between them being found to be quite marginal.