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Question: The most prominent feature of the hydrogen spectrum in the visible region is the red Balmer line, coming from the transition n = 3to n = 2. First of all, determine the wavelength and frequency of this line according to the Bohr Theory. Fine structure splits this line into several closely spaced lines; the question is: How many, and what is their spacing? Hint: First determine how many sublevels the n = 2level splits into, and find Efs1for each of these, in eV. Then do the same for n = 3. Draw an energy level diagram showing all possible transitions from n = 3to n = 2. The energy released (in the form of a photon) is role="math" localid="1658311193797" (E3-E2)+E, the first part being common to all of them, and the E(due to fine structure) varying from one transition to the next. Find E(in eV) for each transition. Finally, convert to photon frequency, and determine the spacing between adjacent spectral lines (in Hz- -not the frequency interval between each line and the unperturbed line (which is, of course, unobservable), but the frequency interval between each line and the next one. Your final answer should take the form: "The red Balmer line splits into (???)lines. In order of increasing frequency, they come from the transitionsto (1) j =(???),toj =(???) ,(2) j =(???) to j =(???)鈥︹. The frequency spacing between line (1)and line (2)is (???) Hz, the spacing between line (2)and (3) line (???) Hzis鈥︹..鈥

Short Answer

Expert verified

The frequency spacing between lines are

6-5=0.99109eVv5-4=3.36109eV4-3=6.5109eV3-2=1.09109eV2-1=3.24109eV

Step by step solution

01

Formula Used

To findand, calculate

E=h

E=E30-E20

02

Find the wavelength

There are transition from n = 3 to n=2 ,

According to Bohr's theory:

E=E30-E20=E11n32-1n22=E119-14

where,E1=-13.6eV

then,E=-13.619-14=1.889eV

h=6.62101.61019=4.1410-15eV/sE=hvv=Eh=1.8894.1410-15=4.561014Hz

The wavelength is

=cv=31084.561014=6.5710-7m

03

Calculate fine structure

To calculate the fine structure:

Efs'=En22mc23-4nj+12

- For=2l=0,1j=12,32we have 2 -levels due to the split of n = 2,

j=12E2'=E222mc23-812+12

Where,E2=E1n2=13.64eVE2'=13.6242(2)(0.511106)3-8=5.6610-5eVj=32,E2,=E222mc23-832+12E2,=13.624220.5111063-82=1.1310-5eV

- For n=3l=0,1,2j=12,32,52we have 3-levels splitting for n =3

j=12

E3,=E322mc23-1212+12

Where,E3=E1n2=13.69eV

E3'=E1n2=13.69eVE3'=13.629220.5111063-12=-2.0110-5eVj=32

E3'=E322mc23-1232+12E3'=13.629220.5111063-6=-6.710-6eV

Forn=3l=0,1,2j=12,32,52

localid="1658383160262" j=52E3'=E322mc23-1252+12E3'=13.629220.5111063-4=2.23106eV

Then, there are six transitions of energies:

E=E30+E3'-E20+E2'=E30-E20-E3'-E2'

We need to calculateE3'+E2'E3'+E2',

TakeE=E3'+E2'

04

Calculate energy in every transition

Calculatein every transition, then:

1.

E3'=E322mc23-12j+12=E129220.5111063-12j+12E2'=E222mc23-8j+12=E124220.5111063-8j+12E4=13.6220.5111061923-12-1423-4=-3.610-5eV

2.

1232E=E3'-E2'E4=13.6220.5111061923-12-1423-4=-8.810-6eV

3.

3212E=E3'-E2'E5=13.6220.5111061923-12-1423-8=-4.9910-5eV

4.

localid="1658384765193" 3232E=E3'-E2'E2=13.6220.5111061923-6-1423-4=-4.610-6eV

5.

5212E=E3'-E2'E6=13.6220.5111061923-4-1423-8=-5.410-5eV

6.

5232E=E3'-E2'E5=13.6220.5111061923-4-1423-4=9.110-6eV

05

Calculate frequency spacing

The transition 1232has frequency less than the unperturbed line,

And the other 5-transitions have higher frequencies.

Then, the frequency spacing can be calculated as:

v6-v5=E6h-E6h=14.1410-155.410-5-4.9910-5=0.99109eV

v5-v4=E5h-E4h=14.1410-154.9910-5-3.610-5=3.36109eV

role="math" localid="1658385405705" v4-v3=E4h-E3h=14.1410-153.610-5-9.110-6=6.5109eV

v3-v2=E3h-E2h=14.1410-159.110-6-4.610-6=1.09109eV

v2-v1=E2h-E1h=14.1410-154.610-6+8.810-6=3.24109eV

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Most popular questions from this chapter

Two identical spin-zero bosons are placed in an infinite square well (Equation 2.19). They interact weakly with one another, via the potential

V(x1,x2)=-aV0(x1-x2). (2.19).

(where V0is a constant with the dimensions of energy, and a is the width of the well).

(a)First, ignoring the interaction between the particles, find the ground state and the first excited state鈥攂oth the wave functions and the associated energies.

(b) Use first-order perturbation theory to estimate the effect of the particle鈥 particle interaction on the energies of the ground state and the first excited state.

Question: Consider the Stark effect (Problem 6.36) for the states of hydrogen. There are initially nine degenerate states, 3/m (neglecting spin, as before), and we turn on an electric field in the direction.

(a) Construct the matrix representing the perturbing Hamiltonian. Partial answer: <300|z|310>=-36a,<310|z|320>=-33a,<311|z|321>=-(9/2)a,,

(b) Find the eigenvalues, and their degeneracies.

Suppose the Hamiltonian H, for a particular quantum system, is a function of some parameter let En()and n()be the eigen values and

Eigen functions of. The Feynman-Hellmann theorem22states that

En=(nHn)

(Assuming either that Enis nondegenerate, or-if degenerate-that the n's are the "good" linear combinations of the degenerate Eigen functions).

(a) Prove the Feynman-Hellmann theorem. Hint: Use Equation 6.9.

(b) Apply it to the one-dimensional harmonic oscillator,(i)using =(this yields a formula for the expectation value of V), (II)using =(this yields (T)),and (iii)using =m(this yields a relation between (T)and (V)). Compare your answers to Problem 2.12, and the virial theorem predictions (Problem 3.31).

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?

Starting with Equation 6.80, and using Equations 6.57, 6.61, 6.64, and 6.81, derive Equation 6.82.

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