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Unformatted text preview: Name _________________________ Exam 1, 2011: CHEM/BCMB 4190/6190/8189 1 Exam 1: CHEM/BCMB 4190/6190/8189 (112 points) Thursday, 8 September, 2011 1 ). In the example (right), the effect of a 90 ( /2) pulse applied along the x axis (90 x ) is shown for a bulk magnetization vector ( M ) at equilibrium (on the z axis). For a, b, d and e below, show the effects of the indicated pulses by drawing the missing (originating or resulting) vectors on the coordinate axes. For c and f, fill in the blank with the correct pulse (angle and axis along which it is applied) that will promote the indicated movement of the bulk magnetization vector (there may be more than one correct answer for each). (12 points) a . d . b . e . c . f . y z x y z x 90 - x y z x y z x 270 x y z x y x y x y x 90 y , 90 - x y z x y z x y z x y z x 90 - y z z z 90 - x 180 x 90 x M y z x y z x Name _________________________ Exam 1, 2011: CHEM/BCMB 4190/6190/8189 2 2 ). In one hour, a 1 H NMR spectrum is acquired with a signal-to-noise (S/N) of 3. How long will it take to acquire a spectrum with a signal-to-noise of 12? Assume the second spectrum is acquired in a manner identical to the first. ( 4 points ) Signal-to-noise (S/N) increases as the square root of the number of scans (S/N NS 1/2 ), and the number of scans is directly proportional to the total acquisition time. In order to increase S/N by a factor of 4 (3 to 12), one would have to acquire 4 2 or 16 times the number of scans. If the original experiment took one hour, the second will take 16 hours. 3 ). For nuclei that possess a magnetic moment, discrete energy levels (Zeeman levels/states) are occupied in the presence of a magnetic field. a. What is the value of the spin angular momentum quantum number, I , for a particular nucleus that has six Zeeman levels? For full credit you will have to explain your reasoning. ( 4 points ) The number of possible Zeeman energy levels is equal to (2I+1), where I represents the spin angular momentum quantum number. If (2I+1) = 6, then I = 5/2. b. If the magnetic quantum number, m , for one of the Zeeman energy levels for a particular nucleus is -2, what is the energy of this Zeeman energy level. ( 2 points ) In general, the energy, E, is described by the following equation: If m = -2, then: c. If the magnetic quantum number, m , for one of the Zeeman energy levels for a particular nucleus is -2, what is the spin angular momentum quantum number for this nucleus? Please explain. ( 4 points ) For a given nucleus, possible values of m are I, I-1, I-2,-I. Thus, if m = 2, the spin quantum number must be integral (not half-integral), and must be > 2....
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This note was uploaded on 11/13/2011 for the course CHEM 4190 taught by Professor Staff during the Fall '08 term at University of Georgia Athens.
- Fall '08