Molecules

Question 1

How are molecules treated

Answer 1

Set of point masses at perpendicular distances from centre

Question 2

How to atoms that lie on axis of rotation contribute to total inertia

Answer 2

They don’t

Question 3

How are axes labelled for moments of inertia

Answer 3

Ic > Ib > Ia

Question 4

Linear rotors

Answer 4

Ic = Ib, Ia = 0

Question 5

What are spherical rotors

Answer 5

Molecules in Td and Oh point groups

Question 6

Spherical rotors

Answer 6

Ia = Ib = Ic

Question 7

Symmetric rotor

Answer 7

Ia = Ib don’t equal Ic

Question 8

Asymmetric rotor

Answer 8

3 different I

Question 9

Oblate symmetric top

Answer 9

Rugby ball shaped, I parallel > I perpendicular

Question 10

Prolate symmetric top

Answer 10

Frisbee shaped, I perpendicular > I parallel

Question 11

What do real molecules have that rigid don’t

Answer 11

Centrifugal distortion constant because as molecules rotate faster bonds stretch and geometries distort

Question 12

Degeneracy for spherical rigid rotor energy levels

Answer 12

(2j + 1)^2

Question 13

Degeneracy for prolate symmetric rigid rotor energy levels

Answer 13

2j + 1

Question 14

Additional degeneracy for prolate symmetric rigid rotors

Answer 14

2(2j + 1) when |K|>0

Question 15

Why must K be < or equal to Ic

Answer 15

It’s a projection of J onto Ic axis

Question 16

Degeneracy for oblate symmetric rigid rotor energy levels

Answer 16

Same as prolate