CHM 3520L/5520L | PHYSICAL CHEMISTRY LABORATORY II | Spring, 2019 |

Post-Lab Assignment: | Sodium Atomic Emission Spectrum | |

Each post-lab assignment is to be written as if placed within a lab report and for a CHM 3520L student | ||

readership. Number the topics, 1-6, as per the assignment below. | ||

1. | It is routine to translate a wavelength uncertainty in spectroscopy to a frequency uncertainty |

according to the conversion equation from wavelength to frequency. When the “frequency” units are

wavenumbers (neither true frequency nor true energy but proportional to both) the wavelength-frequency

relationship isν = 1/λ and the relative errors in both quantities are equal: δλ δν

λ ν

= . Use this relative

error relationship withδλ = 0.0077 nm as the average absolute residual in the monochromator calibration

fit and withδλ = 0.0212nm as the maximum absolute residual. Determine the equivalent average and

maximum values ofδν at the shorter and longer wavelength range of our sodium spectrum, say at 450

nm and at 820 nm. The wavelength residuals stated here resulted from the 2016 argon lamp calibration

of our monochromator.

2. Using the fitted equations from your data analysis, predict the vacuum cm-1 positions for the

diffuse and sharp series emission lines from n=9, 10, 11. The air wavelengths will be only 0.11-0.12 nm

shorter than the corresponding vacuum wavelength values. Identify and label these diffuse and sharp

doublets in the attached sodium spectrum over the 420-445 nm range. Many argon lines also appear in

this spectrum. The expected intensity pattern of these doublets may assist you in the task of their

identification.

3. Identify, for the CHM 3520L/5520L audience, which sodium atomic transitions produce the

principal series in emission, the spectral range over which these transitions are observed and the series

limit (short wavelength limit for the n=∞ transition. What is significant about this series (where else or

how else might one observe it) and its limit?

4. For the CHM 3520L/5520L reading audience, explain the differences between R∞, RH and RNa.

Taking the R∞ value and particle masses from NIST, show your calculation for RNa. How does this

compare to a literature value (cite reference source).

5. Explain why we expect a large quantum defect value δs for the sharp series and a small value δd

for the diffuse series. Qualitatively, relative to δs and δd, explain why a CHM 3520L/5520L student

should expect that the relative magnitude expected for δp for the principal series is δd < δp < δs. Discuss

whether or not experimental findings agree with the expectation and what this agreement or lack thereof

means.

6. Use the vacuum wavenumbers of your observed diffuse and sharp series transitions, along with

the 3p(2P3/2)-3s energy difference (cm-1 value for your shorter wavelength D line), to create a Grotrian

energy level diagram for sodium. You may use a software package or graph paper, but do not crudely

sketch an approximate diagram. If you use graph paper, please do a credible job. Use wavenumbers

(vacuum), cm-1, for the y-axis units. In addition to the ns and nd energy levels your diagram also should

show the 3s ground state at zero energy, the 3p2P3/2 level and the ionization limit. It is not necessary to

show the splitting of the np and nd levels. An example of the expected result is attached to this document

and also is available in Pilot. Text can be written in SigmaPlot with a specific angle relative to a

horizontal placement.

Sodium Emission Spectrum Post-Lab Assignment – 1

Sodium Emission Spectrum Post-Lab Assignment – 2

Sodium Emission Spectrum Post-Lab Assignment – 3