Session M1: AMO IV: Spectroscopy

Quantum Mechanical Description of Dipole-Bound Anions of Molecules and Clusters

Quantum mechanical description of dipole-bound anionic complexes formation is given by means of {\it ab-initio} calculations. The electron affinities and electron detachment energies are determined at the CCSD(T) level of theory for number of molecular clusters. Photoelectron spectra peaks are assigned and the mechanisms for the formation of the anions are elucidated.   

Charge asymmetry of the first excited rotational states of diatomic molecules using explicitly correlated all-particle Gaussian functions

Highly accurate interparticle distances and correlation functions of the HD$^+$ cation in its first rotationaly excited state found in the non-Born-Oppenheimer approach are reported. To describe each state, 8000 explicitly correlated Gaussian functions were used. After careful optimization of the linear and nonlinear parameters, the correlation function, expectation values for interparticle distances, and nuclear correlation functions were computed. The results allow to us explicate the charge asymmetry dependence on the vibrational excitation and the effects of the rotational excitation.   

Thermal near-field: spectroscopy of the resonant enhancement of the local electromagnetic density of states

One of the most universal physical processes shared by all matter at finite temperature is the emission of thermal radiation.~Associated with the well understood far-field radiation and its spectral characteristics, recent theoretical work has shown that the corresponding near-field can exhibit distinct spectral, spatial, resonant, and coherence properties. The electromagnetic local density of states (EM-LDOS) is a fundamental quantity determining these properties. We demonstrate the technique of thermal infrared near-field spectroscopy (TINS) to characterize the unique spatial and spectral properties of the thermal near-field by scattering with a nanoscale probe. In particular, we discuss the observed vibrational and phonon-resonant enhancement and relationship with the underlying EM-LDOS. We also demonstrate the sensitivity of the emitted spectra to local dielectric environment, tip-sample coupling, and antenna effects of the scanning probe tip.   

Measurement of the mobility of barium ions in xenon gas and implications for a next generation $^{136}$Xe double beta decay experiment in high pressure gas

The Enriched Xenon Observatory (EXO) is an experiment which aims to observe the neutrinoless double beta decay of $^{136}$Xe. The measurement of this decay would give information about the absolute neutrino mass. Since this is a very rare decay, the ability to reject background events by detecting the barium ion daughter from the double beta decay would be a major advantage. The barium ions may be detected by laser induced fluorescence spectroscopy. One of our efforts in ``barium tagging'' at Colorado State University has been the fluorescence detection of barium ions in xenon gas. It is important to know how fast the barium ions travel in xenon gas. The results of mobility measurements of barium in xenon gas will be presented. The variation of mobility with xenon gas pressure suggests that some molecular ions are formed when barium ions interact with xenon gas at high pressures. The results indicate that the percentage of molecular ions is greater at higher pressures. The results are of interest for a next generation double beta decay experiment, for schemes involving a $^{136}$Xe gas detector.   

Digital Revolution in Electron Paramagnetic Resonance Spectroscopy

Exponential growth in computing power has reached the level that makes reshaping of electron paramagnetic resonance (EPR) spectroscopy inevitable. An EPR spectrometer, as we know it today, conceptually is not very different from ones that were built 40-50 years ago. It performs two basic types of experiments: (i) continuous wave with magnetic field modulation and (ii) pulse. Both types of experiments produce data that are easy to interpret visually or with minimal data processing. Spectroscopy, microscopy and imaging, driven by the digital progress, are now undergoing a paradigm shift toward a different concept, which is to collect a vast amount of complex data and use a computer to process the data into meaningful results. This approach speeds up an experiment and brings in qualitatively new information. This presentation describes a concept of a digital EPR spectrometer, essential parts of which are an arbitrary waveform generator, high-speed digitizer, personal computer and new data processing algorithms