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fall 09 lm _6 NH3 inversion

# fall 09 lm _6 NH3 inversion - Chem 481L Lab Module#6 Energy...

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Chem 481L Fall 2009 Lab Module #6 Energy potential and vibrational levels of NH 3 inversion Due Date: Noon, Tuesday, October 13 Submit via Blackboard Goal: The purpose of this lab is to apply the skills you developed with H 2 + to the problem of the inversion bend in NH 3 . First, using Spartan, you will build an energy profile of the umbrella inversion bending vibrational mode of ammonia: HHHN dihedrals versus energy. You will then use Mathcad to fit the data to a polynomial. Next, you will use the variational theorem with particle-in-a-box (PIB) wavefunctions as a basis set to calculate the first several wavefunctions (and energies) for NH 3 . Given that this lab is analogous to Lab Modules #4 & 5, you can write your own research questions. Readings: See Blackboard. Lab procedure A. Potential energy curve (energy as a function of dihedral) in Spartan (as in LM#10) Build NH 3 in Spartan. Using the HF 6-31g* basis set, calculate the equilibrium geometry, and measure the equilibrium dihedral for the HHHN atoms. The definition of this dihedral is the angle between the plane formed by the first three atoms (HHH) and the plane formed by the last three atoms (HHN). Be sure to define the dihedral using this order of atoms; to do otherwise would compromise the reproducibility of the measurement. Confirm that the molecule is symmetrical, i.e., that all three dihedrals (H1H2H3N, H2H3H1N, H3H1H2N) have the same value. The inversion bend, then, is a symmetrical stretch in which these dihedrals go from equilibrium value (approx 40 o ) to 0 o

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fall 09 lm _6 NH3 inversion - Chem 481L Lab Module#6 Energy...

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