Instrumental analysis

CHM 454/554 Exam 2
Marta P Estarellas

1. Define the following items:

Non-radiative relaxation loss of energy in a series of small steps while the excitation energy is converted to kinetic energy by collision with other molecules.
Internal conversion intermolecular processes by which a molecules passes to a lower energy electronic state without emission of radiation. It’s a crossoverbetween two states of the same multiplicity.
Inter-system crossingprocess in which there is a crossover between electronic states of different multiplicity.
Doppler broadening the Doppler shifts broad the spectral lines. This phenomenon consists in the increasing or decreasing of the wavelength of radiation emitted or absorbed by a rapidly moving atom depending on if the motion is receding fromthe transducer or toward it. In the flame the environment is hot so the atomic motion occurs in every direction, so there’s Doppler broadening.
Atomization process in which the elements present in a sample are converted to gaseous atoms or elementary ions. The precision and accuracy of atomic methods depend critically on the atomization step and the method of introduction of the sample into theatomization region.
Zeeman correctionzeeman effect is a phenomenon consisting in that, when an atomic vapor is exposed to a strong magnetic field, a splitting of electronic energy levels of the atoms takes place that leads to formation of several absorption lines for each electronic transition. These lines are separated from one another by about 0.01 nm, with he sum of the absorbances for thelines being exactly equal to that of the original line from which they were formed. Zeeman effect instruments provide a more accurate correction for background than other methods.
Degeneracy said when two quantum states are identical and, consequently, their vibrations are the same in energy.
Vibrational relaxation promotion of the molecule to any of several vibrational levels during theelectronic excitation process. Collisions between molecules of the excited species and those of the solvent lead to rapid energy transfer with a minuscule increase in temperature of the solvent.
Quantum efficiencyratio of the number of molecules that luminesce to the total number of excited molecules.
Polarizability measure of the deformability of the bond in an electric field.

2.Polarization and polarizability:
a) Describe the difference between “polarization” and “polarizability”. Which types of spectroscopy depend on changes in polarization, and which depend on changes in polarizability?
The polarization is the orientation of electric charge and electron clouds in a molecule while the polarizability is how tightly charges are bound.
IR absorption requires a change inpolarization. Raman scattering requires a change in polarizability.
b) Suppose you want to measure ammonia (NH3) concentrations. Draw the molecular structure and all molecular vibrations of ammonia and show all molecular vibrations (e.g. “normal modes”) of ammonia. Indicate which vibrations produce a change in polarization, and which produce a change in polarizability.
We have 3N-6 normalmodes of vibration. The vibrations with a change in polarization are going to be IR active and if these vibrations change in polarizability are going to be Raman actives.



3. The width of absorption and emission peaks is different for molecular electronic spectroscopy, molecular vibrational spectroscopy, and atomic spectroscopy.
a) Assuming that identical instruments are used tomeasure peak widths, which type(s) of spectroscopy will have the broadest absorption and emission peaks? Which will have the narrowest absorption and emission peaks?
Atomic methods are potentially highly specific because atomic lines are remarkably narrow. Energy level diagrams suggest that an atomic line contains only a single-wavelength; that is because a line of an electron between two discrete,...