Chapter 2 - Principles of ionization and ion dissociation - part 2

Question 1

Typically, ion dissociations are endothermic, and thus

Answer 1

each fragmentation step consumes some of the ions’ internal energy.

Question 2

In fragmentation, simple bond cleavages cause

Answer 2

radical losses.

Question 3

Rearrangement fragmentations typically lead to losses of

Answer 3

intact neutral molecules.

Question 4

In homolytic bond cleavages, the activation energy of the reverse reaction (E0r) is

Answer 4

close to zero because an ion and a radical are created from the cleavage (very reactive with each other).

Question 5

In heterolytic bond cleavages, the activation energy of the reverse reaction (E0r) is

Answer 5

greater than zero because a very stable neutral molecule is formed from heterolytic cleavage.

Question 6

Kinetic energy release (KER)

Answer 6

A portion of the total excess energy is converted into translational motion of the fragments in the direction of the bond that is cleaved.

Question 7

A larger value of KER is expected when

Answer 7

there is a larger sum of total excess energy (excess energy + reverse activation energy).

Question 8

The observed KER consists of two components,

Answer 8

one from excess energy (Eex), and one from reverse activation energy (E0r).

Question 9

Degrees of freedom effect (DOF)

Answer 9

The ratio of Etrans*/Eex decreases as the size of the fragmenting ion increases.

Question 10

Isotope effects

Answer 10

Any effect exerted by the introduction of isotopes.

Question 11

Intermolecular isotope effects example

Answer 11

Comparing D radical loss from CD4 to H radical loss from CH4.

Question 12

Intramolecular isotope effect example

Answer 12

Comparing H radical to D radical loss from CH2D2.

Question 13

The term “primary kinetic isotope effect” applies if

Answer 13

the effect is exerted on a bond where the isotope itself is involved during the reaction.

Question 14

The kinetic isotope effect for heavier elements

Answer 14

decreases.

Question 15

Isotope effects in mass spectrometry are usually

Answer 15

kinetic isotope effects resulting from different rate constants of bond breaking and bond formation without (kH) or with (kD) a heavier isotope involved, respectively.

Question 16

Kinetic isotope effects are called normal if ____, and inverse if ______.

Answer 16

kH/kD > 1

kH/kD < 1

Question 17

Inverse kinetic isotope effects are

Answer 17

rarely observed.

Question 18

Secondary kinetic isotope effects are observed if

Answer 18

an isotopic label is located adjacent to or remote from the bond that is being broken or formed during the reaction.

Question 19

The critical slope method was developed to

Answer 19

overcome the unpredictability of the actual onset of ionization.

Question 20

An electron monochromator is a device for

Answer 20

selecting nearly monoenergetic electrons from an electron beam.

Question 21

The absorption of UV light by a neutral can result in

Answer 21

electronically excited states that undergo relaxation either by emission of light or by emission of an electron.

Question 22

In photoionization (PI), the ______ serves the same purpose as the energetic electron in EI.

Answer 22

photon

Question 23

The normal procedure to achieve PI is

Answer 23

multiphoton ionization (MUPI)

Question 24

Zero kinetic energy photoelectron spectroscopy is based on

Answer 24

distinguishing excited ions from ground state ions.

Question 25

Kinetic shift denotes the

Answer 25

overestimation of AEs due to the contribution of excess energy in the transition state necessary to yield rate constants larger than 10^6 s^-1.

Question 26

The rate of a first order reaction (change in concentration of precursor ion over time) is solely determined by

Answer 26

the concentration of the precursor ion, and its internal energy.

Question 27

Dimension of a first order reaction

Answer 27

s^-1 (or Hz)

Question 28

In a bimolecular reaction, the rate of a second order reaction is dependent on

Answer 28

both the concentration of the respective molecular ions and that of the neutrals.