Spectroscopy

By Jim Nolen

Introduction-- An Historical Perspective:

    Who would have guessed one hundred and fifty years ago that things so ordinary as light and color might unlock countless mysteries of the atom?  In 1885, before the dawn of quantum mechanics, Johann Balmer developed a simple formula which accurately described the four lowest emission lines of the hydrogen atom (Serway 1202).  Other similar formulas describing the emission of light from hydrogen were developed shortly thereafter: the Lyman series, the Paschen series, and the Brackett series (Serway 1202).  Despite the acuracy of such observations, classical physics could do nothing to explain the dynamics of this close relationship between light and atoms.  At the dawn of the twentieth century, a new era of physics dawned as well.  In 1900, German physicist Max Planck determined a very accurate formula to predict the thermal radiation emitted from a so-called "black body" (Serway 1192).  Furthermore, he reasoned that electromagnetic energy existed in discreet amounts proportional to a constant which became known as Planck's constant (Sandin 73).  Five years later in his Nobel Prize winning paper on the photoelectric effect , Albert Einstein provided a crucial link between this quantization of electromagentic energy and the ionization of atoms (Serway 1194).  These and several other developments (such as the Schodinger equation and the construction of the laser) led the development of modern spectroscopic techniques: using light to probe the energy levels of the atom and of molecules.

    These pages discuss a few modern spectroscopic techniques and demonstrate their usefulness in describing molecular dynamics, atomic energy levels, and quantum mechanical concepts.  The discussion begins with molecular spectroscopy and the dynamics of the CO₂ molecule and CO₂ laser.  The next section is an explanation of two-photon absorption and three-photon ionization as seen in Cesium atoms.  Finally, Raman Spectroscopy is discussed as it relates to four-wave mixing in Sodium vapor.  Each of the experiments described were conducted under the guidance of Dr. Wolfgang Christian in the spring of 1999 for Intermediate Laboratory, Davidson College Department of Physics.  Derek Kverno also participated in the development and analysis of these experiments.

Table of Contents:

References:

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