Emission Spectroscopy in the Undergraduate Laboratory

Simple lab experiments using an inexpensive, solid-state computerized spectrometer can help to introduce students to analytical emission spectroscopy. A series of experiments that employ an Ocean Optics spectrometer, a Windows PC, and a fiber optic pickup are described. Line spectra of mercury and hydrogen can be used for wavelength calibration and, in the case of hydrogen, used to determine the Rydberg constant and the spacing between the energy levels in hydrogen. Continuum sources include tungsten lamps and sunlight. Students can also examine mixed spectra; for example, the spectrum of a fluorescent light shows both line and continuum behavior as does the spectrum of a deuterium lamp. Molecular band emission is studied by obtaining the spectra of fireworks—our students used sparklers. The spectra of red, green, blue, and gold sparklers show both atomic lines and molecular bands. The wavelengths of the atomic lines, in conjunction with some basic reference tables, can be used to identify the composition of the sparkler; molecular bands are more difficult to assign, but are responsible for many of the colors observed. Bands arising from salts of barium, strontium, and copper are responsible for the green, red, and blue colors seen in commercially available sparklers.