Electron-ion collisions play an important role in determining the plasma and chemical properties of the Earth's ionosphere. Using parameters calculated under prior National Science Foundation support, theoretical quantal calculations will be made to determine the atomic state quantum yields resulting from the dissociative recombination of N2+ with an electron, i.e. N2+ + e- leading to N + N. Dissociative recombination generates the N(2D) and N(2P) excited states, upper states of well known ionosphere emission lines. Vibrationally excited ions are present at high abundance in the ionosphere but atomic quantum yields for excited ions have never been determined by theory or experiment. By using a new technique, the project will yield accurate quantum yields for the lowest five ion vibrational levels over the wide range of ionospheric electron temperatures. Calculations will also be performed for the vibrational deexcitation of N2+ by electrons, and for the rotational deexcitation and excitation of N2+ by electrons in the Earth's ionosphere. These processes may have high rate constants. Currently, there is no theoretical or experimental information on this fundamental process. Calculations will also be performed for another molecular species in the ionosphere, NO+, since recent observations found that highly rotationally excited NO+ is present in the upper atmosphere. None of the prior laboratory experiments or theoretical calculations have determined dissociative recombination rate constants and quantum yields for very high rotationally excited NO+. Using techniques similar to those developed for the study of N2+, the dissociative recombination rate constants and quantum yields will be determined for NO+ with high rotational excitation. For relaxed ions, prior experimental studies have disagreed on the electron temperature dependence of the dissociative recombination rate constant. The electron temperature dependence and the quantum yields will be calculated for the full range of ionospheric temperatures. The broader impacts of the project include the convening of an international conference devoted to the latest developments in dissociative recombination research. The 8th Meeting will be held in 2010 at Lake Tahoe, California, with the project providing support for student travel. A website on dissociative recombination is maintained, which provides the rate coefficient data for N2+ for dissociative recombination, vibrational excitation/relaxation and rotational excitation/relaxation and the full set of data that enters the calculations. A section of the website is allotted to explanatory material and an animation for nonexperts.
14.00 Normal 0 false false false EN-US JA X-NONE Intellectual Merit The principal purpose of this research is the study of what happens when a molecule captures an electron it has lost. How does this loss occur? In the Earth’s upper atmosphere, in a region known as the ionosphere, electrons go missing all the time mostly during the day. Light from the Sun impacts this region with enough energy to knock out electrons from molecules. The process repeats daily, starting at every dawn and winding down at every sunset. The electron density would build up day after day if it were not for the removal of these electrons by molecules that have lost electrons to sunlight. The removal is remarkable because a common result is that after capture, the molecule is destroyed in a process known as dissociative recombination (DR). In order to understand the ionosphere, it is necessary to know the probability of electron capture and how it varies with certain molecular characteristics. It is also important to identify the nature of the new products that are formed because they can both emit light and move with very high energies. The supported research has focused on the DR of an important atmospheric molecule, N2+. The plus sign indicates that the molecule is missing an electron. After capture, two N atoms are produced which can emit light at energies that are different from the energy of the light that knocked out the electron. The excited high energy N atoms affect the temperature and chemistry of the ionosphere by initiating other reactions with other molecules. The probability of electron capture varies with the vibrational state of N2+. The two N atoms that compose the molecule vibrate as if they were connected by a spring. The spring is composed of the electrons that bind the two atoms together. The energy of the vibration is quantized and can have only fixed values. In the supported research, techniques in theoretical quantum chemistry have been used to calculate the probability of DR and how it varies with vibrational energy. The calculations are done on powerful computers. In the ionosphere, it is known that N2+ is present in the five lowest energy vibrational levels. The probability of DR by the lowest vibrational level had been measured in laboratory experiments. However, the probability for the next highest 4 levels had never been determined before. The calculations supported by NSF found that the probability for DR by the lowest level agreed with the prior experimental determinations giving us confidence that the calculated values for the upper 4 levels are highly accurate. Another process that can occur in the ionosphere is that electron impact can cause a molecular ion to change its vibrational state. This is very important because the new state can have a very different probability for DR than the prior state. The probability of this process was unknown prior to the NSF supported research. The research showed that the probability of vibrational change cannot be neglected and can be nearly as high as that for DR. An additional focus of the research was upon the identification of the electronic states of the atoms that are generated in DR. The nature of the states that are produced is significantly affected by interactions that take place while the molecule is dissociating. These interactions have been calculated and the yields of products from the lowest vibrational level have been calculated. Theoretical quantum chemical calculations have also started on the DR of NO+, another important ionospheric molecule. The ionosphere is vital to radio communications because the waves are reflected by the electrons. The NSF supported research is essential to the improvement of models that help us understand and predict the response of the ionosphere to solar radiation. Broader Impact In 1988, the PI and one other researcher organized the first of a series of international meetings on DR. The PI organized the 5th meeting in 2001. The PI was a coorganizer of the 9th meeting held at Lake Tahoe, CA in August, 2010. Students and members of underrepresented groups have attended these meetings and NSF has provided support for travel and lodging. A book of refereed papers, coedited by the principal investigator is freely available on the internet. This book describes the latest developments in the field and is aimed at a wide audience.
