The wavelengths of the discrete lines of the atomic spectra of various gases are measured using a grating spectrophotometer.

The atomic spectra of Hydrogen, Helium and Mercury are scanned by hand using a grating spectrophotometer, which measures relative light intensity as a function of angle. From the resulting graph, the wavelengths of the spectral lines are determined by measuring the angle from the central maximum to each line. First and second order lines are examined. The spectrum of Sodium (the Sodium doublet cannot be resolved) is used to calibrate the diffraction grating.

The wavelengths of the spectral lines are compared to the accepted values and, in the case of Hydrogen, the electron orbit transitions corresponding to the lines are identified.

Note: The results are qualitative, and suitable for introductory classes only.

PASCO Advantage:
The open construction of this spectrophotometer allows the entire spectrum to be seen while the intensity versus angle is graphed in real-time.