Chapter 4: Photochemistry and Radiation Chemistry

Question 1

Photochemistry refers to reactions that are ______________.

Answer 1

initiated by interactions of molecules with photon radiation

Question 2

Quantum yield Q is defined as ____________.

Answer 2

the number of entities altered per quantum absorbed

Question 3

nonradiative means _____________.

Answer 3

energy is deposited into the medium but photon/electron is not emitted.

Question 4

Quantum yield is equal to 1 when ____________. Typically Q = ______.

Answer 4

there are no nonradiative processes.
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Question 5

Photosensitization is a process in which a ___________ molecule is photochemically altered via the reaction with _______________.

Answer 5

non-absorbing
excited chromophore-photosensitizer

Question 6

The 5 types of interaction for photosensitization are
1.
2.
3.
4.
5.
This is because the binding of PS changes ____________.

Answer 6

Binding of PS changes the absorption spectrum of A.
Excitation transfer
Electron transfer
Exciplex
Indirect reaction
absorption spectrum of A

Question 7

The excitation transfer sensitized reaction is _______________. The mechanism is _____________.

Answer 7

PS + hv –> PS; PS + A –> PS + A*
the excitation energy is directly transferred from the sensitizer to the acceptor.

Question 8

The electron transfer sensitized reaction is _______________. The mechanism is _____________.

Answer 8

PS* + A –> PS+ + A- or PS* + A –> PS- + A+
the excited molecule transfers or captures an electron, can also be radical ions.

Question 9

The exciplex sensitized reaction is _______________. The mechanism is _____________.

Answer 9

PS* + A –> (PSA) –> PS + A
the excited sensitizer forms a reactive complex with the acceptor

Question 10

The indirect sensitized reaction is _______________. The mechanism is _____________. If O2 is present as _________, then the reaction is for ______________.

Answer 10

PS* + B –> PS + B, B + A –> B + A’
[B* is excited state, reacts with A to alter A to A’]
the sensitizer transfers ts energy to another molecule B which in turn reacts with the acceptor
B
photodynamic therapy (PDT)

Question 11

Sensitized reactions can start both from singlet and triple states, but ________ is more frequent because of _________.

Answer 11

triplet
the longer lifetime

Question 12

A reaction is photosensitized if it is ____________ and _____________.

Answer 12

caused by light
does not occur in absence of the sensitizer

Question 13

Radiation chemistry deals with chemical reactions caused by ____________.

Answer 13

ionizing radiations

Question 14

Contrary to photochemistry, in radiation chemisty _____________.

Answer 14

absorption involves the whole reaction mixture, not just chromophores

Question 15

In radiation chemistry quantum yield is replaced by _________.

Answer 15

G value

Question 16

G value is defined as _____________ or ___________. Typical value is ________ if _________.

Answer 16

number of altered entities per 100 eV absorbed energy
molar concentration of altered entities per unit dose
<= 10
no chain reactions

Question 17

Most energy deposited in cells is absorbed initially by ________ which makes up _________ of the cell.

Answer 17

water
70-80%

Question 18

__________ or _________ occurs when the energy loss of high-energy electrons is absorbed by water.

Answer 18

ionization
excitation

Question 19

The 3 kinds of free radicals formed through radiolysis of water are ____________, __________, and _________.

Answer 19

.OH
e- aq
H.

Question 20

The 4 types of reactions of primary radiolytic products with target molecules are __________, __________, __________, and ___________. ___________ is a major contributor to the damage of biological molecules.

Answer 20

hydrogen abstraction
dissociation
addition reaction
solute radicals form stable products
First