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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

Consider the double delta-function potentialV(x)=-[x+a+x-a]Whereand are positive constants

(a) Sketch this potential.

(b) How many bound states does it possess? Find the allowed energies, for=/maand for=2/4ma, and sketch the wave functions.

A free particle has the initial wave function
(x,0)=Ae-a|x|,

where A and a are positive real constants.

(a)Normalize(x,0).

(b) Find(k).

(c) Construct (x,t),in the form of an integral.

(d) Discuss the limiting cases very large, and a very small.

-consider the 鈥渟tep鈥 potential:

v(x)={0,ifx0,V0,ifx>0,

a.Calculate the reflection coefficient, for the case E < V0, and comment on the answer.

b. Calculate the reflection coefficient, for the case E >V0.

c. For potential such as this, which does not go back to zero to the right of the barrier, the transmission coefficient is not simply F2A2(with A the incident amplitude and F the transmitted amplitude), because the transmitted wave travels at a different speed . Show thatT=E-V0V0F2A2,for E >V0. What is T for E < V0?

d. For E > V0, calculate the transmission coefficient for the step potential, and check that T + R = 1.


A particle in the infinite square well (Equation 2.22) has the initial wave function 唯 (x, 0) = A sin3(蟺x/a) (0 鈮 x 鈮 a). Determine A, find 唯(x, t), and calculate 銆坸銆塧s a function of time. What is the expectation value of the energy? Hint: sinn胃 and cosn胃 can be reduced, by repeated application of the
trigonometric sum formulas, to linear combinations of sin(m胃) and cos(m胃), with m = 0, 1, 2, . . ., n.

Although the overall phase constant of the wave function is of no physical significance (it cancels out whenever you calculate a measurable quantity), the relative phase of the coefficients in Equation 2.17 does matter. For example, suppose we change the relative phase of 1and2in problem 2.5:(x,0)=A[1x+ei2x]Where is some constant. Find (x,t),|x,t|2, and (x), and compare your results with what you got before. Study the special cases =2and=.

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