Spectroscopy Part 1

Question 1

What determined the energy of a photon?

Answer 1

wavelength and frequency

Question 2

What defines polarization in light?

Answer 2

Direction of its electric field

Question 3

What defines polarization in light?

Answer 3

Direction of its electric field

Question 4

What are Fraunhofer lines?

Answer 4

Set of spectral lines originally observed as dark features in the optical spectrum of the sun

Question 5

What is the condition of resonance?

Answer 5

Radiation must have the same energy as a transition between two states

Question 6

Why must there be equal energies between the initial and final states?

Answer 6

To observe absorption in an absorption vs. wavelength graph

Question 7

Which needs a lot of energy: nuclear transitions or nuclear/electron spins?

Answer 7

Nuclear transitions (gamma rays)

Question 8

True or False: the ground state is not thermodynamically stable

Answer 8

False: it is thermodynamically stable

Question 9

How can an atom/molecule end up in an excited state?

Answer 9

Through the absorption of a photon, chemical reaction or including thermal energy

Question 10

What is the most likely transition for a molecule?

Answer 10

HOMO to LUMO

Question 11

What does HOMO stand for?

Answer 11

Highest Occupied Molecular Orbital

Question 12

What does LUMO stand for?

Answer 12

Lowest Unoccupied Molecular Orbital

Question 13

What is Ground State (S0)?

Answer 13

The total spin number is 0 and two electrons of opposite spin are in the HOMO

Question 14

What is the 1st Excited Singlet State (S1)?

Answer 14

The total spin quantum number is 0 and one electron is located in the LUMO and a spin paired electron is located in the LUMO

Question 15

The excited state is ________. The molecule returns to its groud state via the production of heat, light or energy transfer to another molecule (Q)

Answer 15

transient

Question 16

What do ground state-to excited state transition energies depend on?

Answer 16

Molecular structure, intermolecular interactions, and local environment

Question 17

Why is HOMO to LUMO the most common/likely transition state?

Answer 17

Because it has the lowest energy gap

Question 18

What is the difference between 1st Excited Singlet State and the 1st Excited Triplet State?

Answer 18

1st Excited Singlet State: different spin of one electron in the HOMO and another in the LUMO
1st Excited Triplet State: same spin of one electron in the HOMO and another in the LUMO (therefore takes a while to go back to ground state due to the Pauli exclusion principle)

Question 19

Why do molecular moieties likely absorb light in the 200 to 800 nm region?

Answer 19

Because that is the region of the UV vis spectroscopy, which is light we can see

Question 20

What are chromophores?

Answer 20

Part of a molecular entity responsible for an absorption band and the approximate location of the corresponding electronic transition (e.g.: aromatics, alkenes, carbonyls)

Question 21

Conjugation of _________ bonds tends to decrease transition energies

Answer 21

unsaturated

Question 22

What is the Hyperchromic shift?

Answer 22

The strength of absorption (absorptivity)roughly doubles with each new conjugated double bond

Question 23

What are auxochromes?

Answer 23

Chemical group that is attached to a chromophore and modifies its light absorption properties by altering the energies of the MOs