New Physics with Cold Molecules : Precise Microwave Spectroscopy of CH and the Development of a Microwave Trap

Cold polar molecules provide unique opportunities to test fundamental physics and chemistry. Their permanent electric dipole moments and rich internal structure arising from their vibrational and rotational motion, makes them sensitive probes for new physics. These features also make them ideal for studying ultracold chemistry, for simulating the behaviour of strongly interacting many-body quantum systems, and for quantum information science. This thesis describes a number of advances in cold molecule physics. The optimum method for producing an intense, pulsed, supersonic beam of cold CH molecules is investigated, resulting in a beam with 3.5x10^9 ground state CH molecules per steradian per shot. The beam has a translational temperature of 400 mK and a velocity that is tuneable between 400 and 1800 m/s. The lowest-lying Λ-doublet transitions of ground state CH, at 3.3 GHz and 0.7 GHz, are exceptionally sensitive to variations in the fine-structure constant α and the electron-to-proton mass ratio μ. Many modern theories predict that these constants may depend on time, position, or local matter density. Using a novel spectroscopic method, the frequencies of these microwave transitions are measured with accuracy down to 3 Hz. By comparing to radio-astronomical observations, the hypothesis that fundamental constants may differ between the high and low density environments of the Earth and the interstellar medium of the Milky Way is tested. These measurements find no variation and set upper limits of |Δα/α| < 2.1x10^-7 and |Δμ/μ| < 4.3x10^-7. The frequency of the lowest millimetre-wave transition of CH, near 533 GHz, is also measured with an accuracy of 0.6 kHz. The development of a novel type of trap for ground state polar molecules is presented. Trapping polar molecules is a necessary condition to cool them to ultracold temperatures of 1 μK and below. The trap uses a high intensity microwave field in a Fabry-Pérot resonator. Experimental and theoretical investigations are presented that explore the modes of the cavity, how to obtain the highest possible quality factor, and how to optimally couple the microwave power into the cavity. Finally, a cold supersonic beam of BH molecules is developed. This molecule appears to be particularly well-suited to direct laser cooling due to its favourable rotational structure and Franck-Condon factors. The laser cooling concept is described, and a first spectroscopic investigation of the relevant molecular structure is presented.Open Acces

NASA's Upper Atmosphere Research Program UARP and Atmospheric Chemistry Modeling and Analysis Program (ACMAP): Research Summaries 1994 - 1996. Report to Congress and the Environmental Protection Agency

Under the mandate contained in the FY 1976 NASA Authorization Act, the National Aeronautics and Space Administration (NASA) has developed and is implementing a comprehensive program of research, technology, and monitoring of the Earth's upper atmosphere, with emphasis on the stratosphere. This program aims at expanding our understanding to permit both the quantitative analysis of current perturbations as well as the assessment of possible future changes in this important region of our environment. It is carried out jointly by the Upper Atmosphere Research Program (UARP) and the Atmospheric Chemistry Modeling and Analysis Program (ACMAP), both managed within the Science Division in the Office of Mission to Planet Earth at NASA. Significant contributions to this effort are also provided by the Atmospheric Effects of Aviation Project (AEAP) of NASA's Office of Aeronautics. The long-term objectives of the present program are to perform research to: understand the physics, chemistry, and transport processes of the upper atmosphere and their effect on the distribution of chemical species in the stratosphere, such as ozone; understand the relationship of the trace constituent composition of the lower stratosphere and the lower troposphere to the radiative balance and temperature distribution of the Earth's atmosphere; and accurately assess possible perturbations of the upper atmosphere caused by human activities as well as by natural phenomena. In compliance with the Clean Air Act Amendments of 1990, Public Law 101-549, NASA has prepared a report on the state of our knowledge of the Earth's upper atmosphere, particularly the stratosphere, and on the progress of UARP and ACMAP. The report for the year 1996 is composed of two parts. Part 1 summarizes the objectives, status, and accomplishments of the research tasks supported under NASA UARP and ACMAP in a document entitled, Research Summary 1994-1996. Part 2 is entitled Present State of Knowledge of the Upper Atmosphere 1996.- An Assessment Report. It consists primarily of the Executive Summary and Chapter Summaries of the World Meteorological Organization Global Ozone Research and Monitoring Project Report No. 37, Scientific Assessment of Ozone Depletion: 1994, sponsored by NASA, the National Oceanic and Atmospheric Administration (NOAA), the UK Department of the Environment, the United Nations Environment Program, and the World Meteorological Organization. Other sections of Part 11 include summaries of the following: an Atmospheric Ozone Research Plan from NASA's Office of Mission to Planet Earth; summaries from a series of Space Shuttle-based missions and two recent airborne measurement campaigns; the Executive Summary of the 1995 Scientific Assessment of the Atmospheric Effects of Stratospheric Aircraft, and the most recent evaluation of photochemical and chemical kinetics data (Evaluation No. 12 of the NASA Panel for Data Evaluation) used as input parameters for atmospheric models