Lecture 10 (Vibrational Spectroscopy, IR and Raman, etc.)

Question 1

For a vibrational mode to be IR active, it must have a change in _____ of the molecule?

Answer 1

Dipol moment

Question 2

For a vibrational mode to be Raman active, it must have a change in _____ of the molecule?

Answer 2

polarizability

Question 3

What is polarizability ?

Answer 3

The ease with which the molecular electron cloud is distorted

Question 4

Examples of “soft”, easily polarizable elements.

Answer 4

RS-, I-, Hg2+

Question 5

Examples of “hard”, not easily polarizable elements.

Answer 5

F-, Cl-, Li+

Question 6

What is rule of mutual exclusion for centrosymmetric molecules?

Answer 6

Vibrations that are IR active are also Raman active, and vice versa

Question 7

What is the fundamental transition?

Answer 7

The transition from the vibrational ground state to the first excited state

Question 8

A molecule with n atoms has how many degrees of freedom?

Answer 8

3n

Question 9

What are the 3 movements seen in a molecule?

Answer 9

vibrational, translational, rotational

Question 10

How many translational movements are there in a molecule?

Answer 10

3

Question 11

A non-linear molecule with n atoms has how many degrees of rotational freedom?

Answer 11

3

Question 12

A linear molecule with n atoms has how many degrees of rotational freedom?

Answer 12

2

Question 13

A non-linear molecule with n atoms has how many degrees of vibrational freedom?

Answer 13

3n-6

Question 14

A linear molecule with n atoms has how many degrees of vibrational freedom?

Answer 14

3n-5

Question 15

Stretching vibrations are noted as …

Answer 15

ν

Question 16

Bending (deformation) vibrations are noted as …

Answer 16

δ

Question 17

What is it called when vibrations require the same amount of energy?

Answer 17

degenerate

Question 18

For linear triatomic molecules, where masses of substituents are different, the two stretching vibrations can be assigned to individual bonds. True or False?

Answer 18

True

Question 19

For vibrational spectroscopy character tables, what does 1 stand for?

Answer 19

the position does not change

Question 20

For vibrational spectroscopy character tables, what does 0 stand for?

Answer 20

the position changes

Question 21

What is the formula for the Cn symmetry operation?

Answer 21

1+2cos(360/n)

Question 22

What is the formula for the Sn symmetry operation?

Answer 22

-1+2cos(360/n)

Question 23

what does x, y, and z symmetry labels mean?

Answer 23

translational movements

Question 24

What does the Rx, Ry, Rz symmetry labels mean?

Answer 24

Rotational movements

Question 25

What is formula for vibrational movements?

Answer 25

Γvibrational = Γ3N - Γtranslational - Γrotational