Spectrum of the Hydrogen Atom

CHEM 381Fall 2006

Objective

Obtain atomic emission spectra of H, Hg,and Na

Determine calibration curves based onknown Hg and Na line assignments

Assign H emission lines Determine Rydberg constant

Hydrogen Energy Levels

Balmer Series :

Grating Spectrograph

Film Holder

Slit Assembly

Focusing lens

Schematic Diagram of a GratingSpectrograph

1. Light source. 2. cylindrical focusing lens.3. Diffraction grating. 4. Film holder. 5. Slit assembly.

Light Source : Arc lamp

HighpotentialDifference

Hydrogen Lamp

Hot Cathode

Glass tube with H2 gas at very low pressure

Stream of high velocity electrons

What to Do Need to align the arc lamp. Load the film into the holder under dark. Make the exposure as described under . the section Lamps, ch. 5, lab manual. Develop the film. Assign spectral line positions using comparator. Using Matlab routine ‘Experlsq.m’, draw the least square fitting curve for mercury lines and estimate the hydrogen line wavelengths. Calculate Rydberg constant, and analyze the error.

Accessories

Hydrogen lamp,Mercury lamp, and Nalamp

Comparator

Film DevelopingChemicals, tank

Safety Measures

Both arc lamps operate at extremely highvoltage. Need to handle carefully.

Do not look directly at the Hg lamp, since itemits UV radiation.

Na lamp gets extremely hot while it is inuse.

Imaging Spectra

3. Hydrogen5. Hydrogen, Mercury, Sodium7. Mercury9. Sodium

Image placementsetting

Comparator

MATLAB Fit for Hg LinesH Emission λ vs. Comparator Position

Examples

Final Report

All data. (comparator + known/unknownwavelengths)

Tables for measured H and Hg line positions.Analysis methods.Sample calculations, and film.All relevant graphs and MATLAB scripts.Error Analysis* for H wavelengths and R.Estimated value for the Rydberg constant.