Lecture 6 - Collisional Excitation

Question 1

Why is collisional excitation important?

Answer 1

It cools. Collision excites, causing radiative losses

Question 2

Infrared “forbidden lines” emission comes from what gas?

Answer 2

Warm HI (T~5000K)

Question 3

What temperature does 1 eV correspond to?

Answer 3

About 10 000 K

Question 4

Supersonic collisions creates a type of heating known as…

Answer 4

shock heating

Question 5

For what gas is recombination an important source of radiation?

Answer 5

HII regions. (This is not due to collisional excitation though)

Question 6

In some cases radiation can be used to infer three things, what?

Answer 6

density, temperature and radiation field

Question 7

What is the W-factor?

Answer 7

The W-factor is how close the electron has to be to cause de-excitation of an ion (in terms of the Bohr radius)

Question 8

What letter denotes the total angular momentum / hbar ?

Answer 8

J

Question 9

What’s the degeneracy for atoms and ions?

Answer 9

2J+1

Question 10

What is hyperfine splitting?

Answer 10

Interaction of electrons with nuclear magnetic moment

Question 11

What is Zeeman splitting?

Answer 11

Interaction of electrons with an applied magnetic field

Question 12

What is Stark splitting?

Answer 12

Interaction of electrons with an applied electric field

Question 13

An allowed transition obeys ___ transition rules for electric dipole transitions

Answer 13

all

Question 14

Spin-forbidden (transitions) synonym

Answer 14

semi-forbidden, intercombination (transitions)

Question 15

Forbidden transitions criterion

Answer 15

Fail to fulfill at least one of the selection rules apart from ‘spin does not change’