Class Notes (839,394)
Canada (511,324)
Chemistry (614)
CHEM 121 (131)

Selection Rules for Atomic Spectroscopy

2 Pages

Course Code
CHEM 121
Jackie Stewart

This preview shows 80% of the first page. Sign up to view the full 2 pages of the document.
Chemistry 121 2007 Selection Rules for Atomic Spectroscopy When an atom or ion is excited or de-excited in an absorption or emission experiment an electron undergoes a change of state from one orbital to another. The two orbitals involved are described by a set of four quantum numbers, n, l, m and m . lhe firstsconsid eration in deciding which transitions are allowed is that of conservation of energy. This requires that the energy of the photon (E photon= hν photon) is equal to the energy difference (∆E) between the two orbitals is the same as the energy of the photon. Therefore, th e principal quantum number can change by any amount consistent with the energy change of the tr ansition. This princip le leads us to our first selection rule. A selection rule is a statem ent about th e transitions that ar e allowed. W e can write a selection rule for any transition as follows, ∆n = n -fn =ianything consistent with energy conservation where n and n are the principal quantum numbers for the initial and final states respectively. i f We now have to consider any possible constrai nts on the other quantum numbers. The angular momentum quantum number, l, describes the type of orbital th at th e elec tron is in. In an excitation or de-excitation the angular momentum can change as follows, ∆l = lf– li The question is, by how much can ∆l change? The answer lies in the fact that a photon has an intrinsic spin angular mom entum of one (1) unit and that angular m omentum has to be conserved. This requires that ∆l = l – l = angular momentum of the photon= ± 1 f i where the positive sign corresponds to the abso rption of a photon and the negative sign to the emission of a photon. In summary the change in an
More Less
Unlock Document

Only 80% of the first page are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.