Chem 125 Lecture 8 9/19/08 This material is for the exclusive use of Chem 125 students at Yale and may not be copied or distributed further. It is not readily understood without reference to notes from the lecture.

Exam 1 - Friday, Sept. 26 ! Covers Lectures through Wednesday Including: Functional Groups X-Ray Diffraction 1-Dimensional Quantum Mechanics & 1-Electron Atoms (Sections I-V of quantum webpage & Erwin Meets Goldilocks)Erwin Meets Goldilocks Exam Review 8-10 pm Wednesday, Sept. 24, Room WLH ??? Come with questions.

From “Jeopardy” Approach to Recipe for Solution of Schr ö dinger Equation Using Guessed Energies

Rearranging Schr ö dinger to give a formula for curve tracing. C  Curvature of  m + V = E C  Curvature of  m (V- E) = Curves away from 0 for V>E; toward 0 for V<E. Since m, C, V(x) are given, this recipe allows tracing  (x) in steps, from initial  (0) [= 1], with initial slope [0], and a guessed E.

100 kcal/mole 2.5Å 0 Nodes and Quantization in One Dimension from Erwin Meets Goldilocks (for Wiki see Monday Problem Set) Too Cold Too Hot Just Right! kcal/mole Guess 21 kcal/mole Guess 20 kcal/mole Danger Negative Kinetic Energy (Curve Away from Baseline) Danger Negative Kinetic Energy (Curve Away from Baseline) Erwin Meets Goldilocks

100 kcal/mole 2.5Å kcal/mole Erwin Meets Goldilocks Could there be a lower-energy Psi? 4.15 kcal/mole kcal/mole Could there be an energy between? NODES 0 because of sign change More Energy  More Curvature  More Nodes

Much Harder for Many Particles Is it worth our effort?

Reward for Finding  Knowledge of Everything e.g. Allowed Energies Structure Dynamics Bonding Reactivity

Harmonic Spacing Even Energy Spacing for Hooke’s Law E = k (n- ) 1 2

“We only wish that we could glean an inkling of what  could mean.”

Structure:  2  Probability Density Max Born (June 25, 1926) If one wishes to translate this result into physical terms, only one interpretation is possible,  signifies the probability [of the structure] 1 ) Correction in proof: more careful consideration shows that the probability is proportional to the square of the size of . 1)1) Oops!

Structure:  2  Probability Density Aber eine innere Stimme sagt mir, dass das doch nicht der wahre Jakob ist. Die Theorie liefert viel, aber dem Geheimnis des Alten bringt sie uns kaum n ä her. Jedenfalls bin ich ü berzeugt, dass der nicht w ü rfelt. But an inner voice tells me, that this is not the real thing. The theory yields a great deal, but it brings us no nearer to the secret of the Old One. Anyway I am convinced that He does not play dice. Albert Einstein to Max Born December 4, 1926

Probability Density Suppose the total mass in the flask is 1 kg. How much (or what fraction) is exactly 1 cm from the bottom? Multiply density by volume for mass (or fraction, or probability). 0 !

“Normalization” Scale  so that total (integral of)   2  volume = 1

Harmonic Probability Ultimately Probability Builds Up at the Extremes 1.5 Å (not normalized!) Probability Penetrates the Classically ‘Forbidden’ Region

Morse Quantization Morse Potential : Quantized; Probability Spreads to Right Because low kinetic energy means low curvature 7 Å ~ Exponential Decay (e -x ) (~ constant negative kinetic energy) Total Potential Kinetic

Morse Quantization Morse Potential : Quantized; Probability Spreads to Right Energies not evenly spaced as for Hooke’s Law 7 Å As the energy increases, along with the number of nodes, the well widens more than it would for a Hooke’s Law parabola. Thus wavelengths become longer, and energies lower, than expected for Hooke’s Law.

Morse Continuum Morse Potential : Not Quantized above Dissociation Limit ~ sin(x) (~ constant positive kinetic energy) Total Potential Kinetic

Coulombic Spacing 50 Å One-dimensional e - in Coulombic Potential of a Proton ! High Curvature (Erwin Program is approximate)

Coulomb Three E = k n2n2 50 Å Higher levels spread way out

Reward for Finding  Knowledge of Everything e.g. Allowed Energies Structure Dynamics Bonding Reactivity

Change mass Single-bonded H Increase mass from 1 to 14 (H to C 14 ) C  Curvature of  m Greater mass means more curvature for the same energy.

Change mass Single-bonded H Increase mass from 1 to 14 (H to C 14 ) Need to lower energy (curvature) for m=14 C  Curvature of  m Greater mass means more curvature for the same energy.

Mass Effect What about U 235 or a marble? m = 1 m = 14

Mass Effect and Vibration C H Higher-energy H shifted to right in unsymmetrical Morse Potential. half-maximum probability density

Mass Effect and Vibration H C

H C H C ±0.05Å (3% of X-C) ±0.1Å (9% of X-H)

Dunitz et al. (1981) Typically vibrating by ±0.050 Å in the crystal

End of Lecture 8 Sept 19, 2008