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Homework Help: Mechanical Energy of Amonia Molecule

  1. Nov 25, 2009 #1
    Mechanical Energy of Amonia Molecule [SOLVED]

    1. The problem statement, all variables and given/known data
    The ammonia molecule has the tetrahedral structure shown in the figure (Intro 1 figure) . The three hydrogen atoms form a triangle in the xy-plane at z = 0. The nitrogen atom is the apex of the pyramid. The figure (Intro 2 figure) shows the potential energy of the nitrogen atom along a Z-axis that is perpendicular to the H3 triangle.

    A.)At room temperature, the nitrogen atom has .4*10^-20J of mechanical energy. Describe the position and motion of the nitrogen atom.

    B.)The nitrogen atom can gain energy if the molecule absorbs energy from a light wave. Describe the motion of the nitrogen atom if its energy is 2*10^-20J.

    2. Relevant equations
    Figure 1:
    http://img694.imageshack.us/img694/6085/10p60a.jpg [Broken]
    Figure 2:
    http://img294.imageshack.us/img294/5705/10p60b.jpg [Broken]

    3. The attempt at a solution

    Absolutely no idea! >.<
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Nov 25, 2009 #2


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    Homework Helper

    The nitrogen atom is confined in the potential well shown in the figure. Draw a horizontal line at hight of the total energy: this line represents the motion of the atom inside the potential well. It can not go over the blue line, but moves periodically between the borders of the well. At the position z where the horizontal line crosses the blue line, the atom has no KE. At other positions, its KE is the difference of the total energy and the potential energy.

    In the first case, the atom moves either in the left or in the right well, as it s energy is lower than the barrier of about 1.2 x10-20 J. If the energy is 2x10-20 J the N atom crosses the plane of the three hydrogen atoms during its motion.

  4. Nov 26, 2009 #3
    Thanks, I think I understand the problem now!
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