Explain the excitation and emission processes

Question

Question 1: Which of the following represents a hardware strategy to increase signal to noise ratio?

a. Ensemble averaging

b. Fourier filter

c. Faraday cage

d. Background subtraction

Question 2: Why are atomic emission lines sharp, whereas molecular fluorescence lines are broad?

a. Because you measure atomic emission at very high temperatures and molecular fluorescence is normally measured at room temperature

b. Because atoms disperse energy by collisions with other atoms, which is more frequent than molecular collisions

c. Because molecules consist of several atoms whose fluorescence overlaps, whereas atoms emit only a single emission line.

d. Because molecules can be excited into vibrational states, whereas atoms don't undergo vibrations

Question 3: Which X-ray spectroscopy technique measures emitted valence electrons due to electronic relaxation of the sample?

a. X-ray Photoelectron Spectroscopy

b. Auger Electron Spectroscopy

c. X-ray Fluorescence Spectroscopy

d. X-ray Absorption Spectroscopy

Question 4: Raman spectroscopy uses a visible or near-IR laser source but Raman spectra are typically being plotted in the range from about 100 to 4000 cm-1, which is well within the IR range. Why?

a. Raman emission occurs in the IR light range

b. The laser light is in elastically scattered in the infrared region

c. The plotted data represents an energy shift from the excitation laser. This shift has the same energy magnitude as IR light

d. We are measuring Stokes lines, which lie at lower energy than the excitation laser and therefore in the IR region

Question 5: Which of the following processes is NOT associated with X-ray spectroscopies?

a. The emission of a core electron

b. The emission of an Auger electron

c. The emission of an X-ray photon

d. The emission of an IR photon

Question 6: H₃PO₄ is a triprotic acid with pK_a1 = 2.1, pK_a2 = 7.2 and pK_a3 = 12.4. Sketch the speciation plot of this acid through all its species in the diagram below and identify the plotted graphs. Determine the dominant species at pH=10.

Question 7: You have measured light intensities of your incoming light beam with I₀ = 50.000 mW and after passing 1cm of your sample solution I₁ = 0.820 mW. The blank has shown an absorbance of 0.232. Calculate the concentration of your species, given an extinction coefficient at the measured wavelength of 121 M^-1 cm^-1. Show your calculations. Be mindful of significant figures.

Question 8: The signal to noise ratio in Raman spectroscopy is often affected by fluorescence background. Describe the origin of this background, explaining the excitation and emission processes. Give an example of how you can reduce this background.

Question 9: Describe the general composition of a FTIR spectrometer. What is the purpose of the interferometer?

Question 10: The block diagram below describes the setup of an X-ray absorption spectrometry instrument. Describe and justify the likely purpose of the two ionization chambers.

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