Laser Spectroscopy of the Potassium Dimer: Photodissociation Dynamics and Laser-Induced Fluorescence.

Laser spectroscopy is a powerful tool in terms of unraveling both spectroscopic information and dynamic information (e.g. photodissociation). In the first part of this thesis we utilize the polarization of light emitted by the atomic product K* after photodissociation (of K _2). This elucidates the dynamics of photodissociation with emphasis on the "near threshold effects". In the second part of this thesis, we examine the near dissociation region of the K_2 ground state using bound-bound and bound-free A ^1Sigma_sp{rm u} {+} to X ^1Sigma_sp{rm g}{+ } emission. First a linearly polarized tunable CW dye laser was used to excite K_2, in an effusive molecular beam, from the ground X^1Sigma _sp{rm g}{+} state into the continuum of the B^1Pi_ {rm u} state. Resulting photodissociation produces excited atomic K(^2P _{3/2}) which radiates on the D _2 fluorescence line. As the laser is tuned through the molecular bound-free absorption profile, the polarization of atomic fluoresecence was observed ranging from plus 15 +/- 2% to minus 6.3 +/- 0.4%. This appears to be the first observation of such a large variation in the polarization as a function of laser excitation frequency. The K _2 photodissociation theory is presented together with computations concerning final atomic state populations, bound-free excitation profiles and polarization as a function of laser excitation wave-length. The results are most consistent with an adiabatic model for the dissociation near threshold. However, there are significant discrepancies between these model results and the experimental observations when hyperfine depolarization effects are included in the calculation. The origin of these discrepancies is not understood. The polarization profile can be explained in terms of molecular rotation during dissociation. Secondly a single mode ring-dye laser was used to excite rovibronic levels of the K_2 A^1Sigma_sp{rm u }{+} electronic state. The resulting laser induced fluorescence spectra consist of series of R-P doublets and a structured continuum with a maximum at ~1.05mum. An analysis of the spectrum extends the ground state potential energy curve out to 9.614A and predicts the dissociation energy to be D_{rm e}^ {''} = 4457+/- 8cm ^{-1}. Using spectroscopic constants of the A^1Sigma_sp {rm u}{+} state, a bound -free simulation is done. The calculated spectra, which illustrate an interference structure, are in good agreement with the observed spectra.