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Prove Kramers' relation:

sn2rs-(2s+1)ars-1+s4[(2l+1)2-s2]a2rs-2=0

Which relates the expectation values of rto three different powers (s,s-1,ands-2),for an electron in the state n/mof hydrogen. Hint: Rewrite the radial equation (Equation) in the form

u''=[l(l+1)r2-2ar+1n2a2]u

And use it to expressrole="math" localid="1658192415441" (ursu'')drin terms of (rs),(rs-1)and(rs-2). Then use integration by parts to reduce the second derivative. Show that (ursu'')dr=-(s/2)(rs-1)and(u'rsu')dr=-[2/s+1](u''rs+1u')dr. Take it from there.

Short Answer

Expert verified

The proved Kramer鈥檚' relation of equation

rs-2a2s4(2l+1)2-s2-(2s+1)ars-1+s+1n2rs=0

Step by step solution

01

Determine the formula for Kramer's relation

The Kramer鈥檚' relation is a relationship between the anticipated values of "nearby" powers of r for the hydrogen atom, named after the Dutch scientist Hans Kramers:

s+1n2rs-(2s+1)ars-1+a2s4(2l+1)2-s2rs-2=0

02

use the Bohr radius to rewrite the radial portion of the Schrodinger equation

Need to establish a relation:

s+1n2rs-(2s+1)ars-1+a2s4(2l+1)2-s2rs-2=0

Which is equal to a=4蟺蔚o2me2. Radial part of Schrodinger equation:

-u''+-e2402m21r+l(l+1)r2u=E2m2uE=-m22e2401n2-u''+-2ar+l(l+1)r2u=-1a2n2uu''=2ar+l(l+1)r2+1a2n2u

Calculate the following integral using the given hint:

(ursu'')dr=urs-2ar+l(l+1)r2+1a2n2udr=-2aurs-1udr+l(l+1)urs-2udr+1a2n2ursudr=-2ars-1+l(l+1)rs-2+1a2n2rs

But I'm still stumped on the left-hand side of the equation. Use partial integration in this case:

(ursu'')dr=ursu'|0-ddr(urs)u'dr=-(u'rs+surs-1u'dr=-u'rsu'dr-surs-1u'dr

And you'll have to do it twice more for these new unknown integrals:

ursu'dr=-ddr(urs)udr=-u'rsudr-srs-1

u'rsudr=ursu'drBecause radial functions are real, not complex.

2u'rsudr=-srs-1ursu'dr=-s2rs-1

03

Calculate first integral in equation u'rsu'dr-s  urs-1u'dr

In the equation, the first integral must be calculated. This is how we go about it:

(u''rs+1u')dr=-u'ddr(rs+1u')dr=-(s+1)u'rsu'dr-u'rs+1u''dr2(u''rs+1u')dr=-(s+1)u'rsu'dr

u'rsu'dr=-2s+1(u''rs+1u')dr

u''=-2ar+l(l+1)r2+1a2n2uu'rsu'dr=-2s+1-2ar+l(l+1)r2+1a2n2urs+1u'dr=-2s+1-2aursu'dr+l(l+1)urs-1u'dr+1a2n2urs+1u'dr

Using equation get:

u'rsu'dr=-2/s+1)sars-1+l(l+1)-s-12rs-2-1a2n2s+12rs=-2ass+1rs-1+s-1s+1l(l+1)rs-2+1n2a2rs

Equation on second page is:

(ursu'')dr=-u'rsu'dr-surs-1u'dr

On the left hand side, there is an equation from the second page, and on the right hand side, there are equations from the third page and an equation from the second page. All of those equations are now inserted into the previous expression:

-2ars-1+l(l+1)rs-2+1a2n2rs=2ass+1rs-1-s-1s+1l(l+1)rs-2-1n2a2rs+s(s-1)2rs-2rs-2l(l+1)1+s-1s+1-ss-12rs-1ss+1+1+2a2n2rs=0rs-2l(l+1)2ss+1-ss-122ar12s+1s+1+2a2n2rs=0a2(s+1)2

rs-2a2l(l+1)s-s(s2-1)4-(2s+1)ars-1+s+1n2rs=0rs-2a2s4(2l+1)2-s2-(2s+1)ars-1+s+1n2rs=0

The proved Kramer鈥檚' relation of equation

rs-2a2s4(2l+1)2-s2-(2s+1)ars-1+s+1n2rs=0

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Most popular questions from this chapter

(a) Plugs=0,s=2, and s=3into Kramers' relation (Equation 6.104) to obtain formulas for (r-1),(r),(r-2),and(r3). Note that you could continue indefinitely, to find any positive power.

(b) In the other direction, however, you hit a snag. Put in s=-1, and show that all you get is a relation between role="math" localid="1658216018740" (r-2)and(r-3).

(c) But if you can get (r-2)by some other means, you can apply the Kramers' relation to obtain the rest of the negative powers. Use Equation 6.56(which is derived in Problem 6.33) to determine (r-3) , and check your answer against Equation 6.64.

Sometimes it is possible to solve Equation 6.10 directly, without having to expand 1nin terms of the unperturbed wave functions (Equation 6.11). Here are two particularly nice examples.

(a) Stark effect in the ground state of hydrogen.

(i) Find the first-order correction to the ground state of hydrogen in the presence of a uniform external electric field (the Stark effect-see Problem 6.36). Hint: Try a solution of the form

(A+Br+Cr2)e-r/acos

your problem is to find the constants , and C that solve Equation 6.10.

(ii) Use Equation to determine the second-order correction to the ground state energy (the first-order correction is zero, as you found in Problem 6.36(a)).

Answer:-m(3a2eEext/2h)2

(b) If the proton had an electric dipole moment p the potential energy of the electron in hydrogen would be perturbed in the amount

H'=-别辫肠辞蝉胃400r2~

(i) Solve Equation 6.10 for the first-order correction to the ground state wave function.

(ii) Show that the total electric dipole moment of the atom is (surprisingly) zero, to this order.

(iii) Use Equation 6.14 to determine the second-order correction to the ground state energy. What is the first-order correction?

Consider the isotropic three-dimensional harmonic oscillator (Problem 4.38). Discuss the effect (in first order) of the perturbation H'=位虫2yz

(for some constant ) on

(a) the ground state

(b) the (triply degenerate) first excited state. Hint: Use the answers to Problems 2.12and 3.33

Question: Use the virial theorem (Problem 4.40) to prove Equation 6.55.

If I=0, then j=s,mj=ms, and the "good" states are the same (nms)for weak and strong fields. DetermineEz1(from Equation) and the fine structure energies (Equation 6.67), and write down the general result for the I=O Zeeman Effect - regardless of the strength of the field. Show that the strong field formula (Equation 6.82) reproduces this result, provided that we interpret the indeterminate term in square brackets as.

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