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This is a strictly qualitative problem-no calculations allowed! Consider the "double square well" potential (Figure 2.21). Suppose the depth V0and the width a are fixed, and large enough so that several bound states occur.

(a) Sketch the ground state wave function 1and the first excited state localid="1658211858701" 2(i) for the case b = 0 (ii) forbaand (iii) for ba

(b) Qualitatively, how do the corresponding energies(E1andE2)and vary, as b goes from 0 to ? Sketch E1(b)and E2(b)on the same graph.

(c) The double well is a very primitive one-dimensional model for the potential experienced by an electron in a diatomic molecule (the two wells represent the attractive force of the nuclei). If the nuclei are free to move, they will adopt the configuration of minimum energy. In view of your conclusions in (b), does the electron tend to draw the nuclei together, or push them apart? (Of course, there is also the internuclear repulsion to consider, but that's a separate problem.)

Short Answer

Expert verified

(a)The sketch is

(i)

(ii)

(iii)

(b) The graph with and is,

(c)The electron forces the nuclei apart in the first excited state.

The ground state has the lowest energy in configuration I, and with b, the electron tends to attract the nuclei together, enhancing atom bonding.

Step by step solution

01

Define the energy

Power is generated by the use of physical or chemical resources, particularly to create light and heat or to operate machines.

02

Step 2: Draw the graph

(a)

Consider the potential graph shown below. If b=0 , the issue will be a standard finite square well with exponential decay outside and sinusoidal decay within. As a result of the potential's symmetry at the origin, the first solution is cosine, while the second is sine. There is only one node for the sine and none for the cosine.

  1. For b=0




2. For ba Even ground condition. Outside, sinusoidal inside the wells, and hyperbolic cosine inside the barrier. The oddest initial excited state is a hyperbolic sine in the barrier. One without a node 1 and two with a node 2.


3. For b a Similar to (ii), the wave function in the barrier area is quite small. Essentially, there are two isolated finite square wells named and , which are even and odd linear combinations of the two distinct wells' ground states and are degenerate (in energy).



03

Step 3: Graph the values of E1(b) and E2(b)

(b)

When b is close to a in the second scenario, the exponential decay outside, sinusoidal inside the wells, and hyperbolic cosine inside the barrier all signify that the ground state is even. Odd, which in barrier terms denotes hyperbolic sine, describes the first excited state. There are no nodes for 1and 2, respectively.

04

Action of the electron

(c)

Here when b = 0 the energies above the bottom are shown:

En+V0n22h22m2a2

so,

E1+V02h22m2a2E2+V042h22m2a2

For bathe width of each well is a,

E1+V0E2+V02h22ma2

Where:

h=2h22ma2

The ground state has the lowest energy in configuration I, and with b, the electron tends to attract the nuclei together, enhancing atom bonding.

Therefore, the electron, on the other hand, forces the nuclei apart in the first excited state.

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Most popular questions from this chapter

A particle of mass m is in the ground state of the infinite square well (Evaluation 2.19). Suddenly the well expands to twice its original size 鈥 the right wall moving from a to 2a 鈥 leaving the wave function (momentarily) undisturbed. The energy of the particle is now measured.

  1. What is the most probable result? What is the probability of getting that result?
  2. What is the next most probable result, and what is its probability?
  3. What is the expectation value of the energy? (Hint: if you find yourself confronted with an infinite series, try another method)

a) Show that the wave function of a particle in the infinite square well returns to its original form after a quantum revival time T = 4ma2/蟺~. That is: 唯 (x, T) = 唯 (x, 0) for any state (not just a stationary state).


(b) What is the classical revival time, for a particle of energy E bouncing back and forth between the walls?


(c) For what energy are the two revival times equal?

A particle is in the ground state of the harmonic oscillator with classical frequency , when suddenly the spring constant quadruples, so '=2, without initially changing the wave function (of course, will now evolve differently, because the Hamiltonian has changed). What is the probability that a measurement of the energy would still return the value 2? What is the probability of getting ?

In Problem 2.21 you analyzed the stationary gaussian free particle wave packet. Now solve the same problem for the traveling gaussian wave packet, starting with the initial wave function.(x,0)=Ae-ax2eilx

Prove the following three theorem;

a) For normalizable solutions the separation constant E must be real as E0+iand show that if equation 1.20 is to hold for all t, must be zero.

b) The time - independent wave function localid="1658117146660" (x) can always be taken to be real, This doesn鈥檛 mean that every solution to the time-independent Schrodinger equation is real; what it says is that if you鈥檝e got one that is not, it can always be expressed as a linear combination of solutions that are . So, you might as well stick to 鈥檚 that are real

c) If is an even function then (x)can always be taken to be either even or odd

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