Chapter 17 - Fundamental to Spectroscopy

Question 1

Electromagnetic radiation (light) has ____ like properties and ________ like properties

Wave-Particle Duality

Answer 1

wave, particle

some properties of light are best described by as a wave while others as a particle

Question 2

Wave is characterized by its

Distance between successive peaks in a wave
- expressed as units of length: usually nanometers

vertical height of a crest
- determines the light’s intensity or brightness

Answer 2

amplitude and wavelength

wavelength

amplitude

Question 3

Light is also characterized by _______

Number of waves passing a fixed point in a given period of time
- units are cyles per second (1/s) or Hertz

wavelength and frequency are ______ _______

Answer 3

frequency

frequency

inversely related

Question 4

As wavelength decrease, energy and frequency ______

As wavelength increases, energy and frequency _____

Answer 4

increase

decrease

Question 5

something is quantized if it can have only particle values

Energy is ____ to frequency

Answer 5

Quantization

proportional

Question 6

the lowest energy state for a molecule

when a molecule absorb a photon, energy of molecule ______
- molecule is promoted to a ____ ______

when molecule emits a photon, the energy is _________

Answer 6

ground state
- excited state

lowered back down to ground state

Question 7

1. electron moves from one orbital to another
   a. electron has a opposit spin of it’s paired electro then it’s a ______
   b. if the electron has a parallel spin of it’s paired electron the it’s a ______

Answer 7

electron transition

a. singlet state
b. triplet state

Question 8

_____ and _____ don’t have enough energy to cause an electronic transition
- they can change the _____ or _____ motion of the molecule

if a molecule undergoes an electronic transisition, it also undergoing ____ and _____ transitions as well

Answer 8

infrared and microwave
- vibrational, rotational

vibrational, rotational

Question 9

What happens to absorbed energy?:

After absorption to ____ to ____, _____ ______ is the first thing occur first

Answer 9

S0 to S1, vibrational relaxation

Question 10

When vibrational relaxation happens:

a. it brings the molecule down to the lowest vibrational level of ____
b. then it would ____ back down to ____ which is called _____

Answer 10

a. S1

b. emits, S0, fluorescence

Question 11

If the molecule was super excited into S2, it may go through _________ to relax down to ______.

The molecule could also cross over to an excited vibrational level, ____, which is called ______
- it would eventually go back to S0, which is ______

Answer 11

interval conversion, S1

T1, intersystem crossing
- phosphorescence

Question 12

The Jablonski - The Process:

a. transition from the singlet ground to an excited singlet state
- is fast - 10^-15 second

b. when an excited electron relaxes through several vibrational levels within the same electronic level
- sometimes called _______ _________
- pretty fast (10^-14 to 10^-11 seconds)

Answer 12

absorption

vibrational relaxation
- nonradiative decay

Question 13

when an electron relaxes from excited sisate to a lower electronic state without emitting light

• also called ______ ______ ______
• result in energy being transformed into _____
• 10^-14 to 10^-11 seconds

when an electron transition nonradiative from singlet to a lower triplet state

Answer 13

internal conversion

• radiation-less radiative
• heat

intersystem crossing

Question 14

the relaxation from an excited triplet to ground state

• occurs with a very lowe by ______ probability
• how long does take to occur?

the allowed transition from excited singlet to ground singlet
10^-9 to 10^-7 seconds

Answer 14

phosphorescence

• nonzero
• takes much longer

fluorescence

Question 15

measure the transmission of light

a sample is hit by a light
- _____ (P or I): Energy per second unit area of the light beam

a select wavelength of light used

strikes sample and ____ is measured

transmittance is converted to ________

Answer 15

spectrophotometer

irradiated
- irradiance

monochromatic

transmittance

absorbance

Question 16

fraction of original light that passes through the sample
- has a range of 0 to 1

the negative logarithm of its transmittance

if all the light is absorbed, transmittance is ___
- percent transmittance ranges from __% to ___%

Answer 16

Transmittance (T)

Absorbance (A)

0
- 0 to 100

Question 17

The color we see is _____ and colors we don’t see ____

molecule responsible for light absorption is called

Answer 17

transmitted, absorbed

chromophore

Question 18

A relationship relating absorbance to concentration, path length, and molar absorptivity.

\_\_\_\_  is a dimensionless number.
 is a proportionality constant. 
 is path length and has units of length (cm).
Sometimes “b” is used.
is concentration in units of Molarity.

Answer 18

Beer-Lambert Law

A (Absorbance)
ε (molar absorbitvity)
L (path length)
C (concentration)

Question 19

Absorbance is ______ to molar absorptivity
- called the _____ coefficient

It is a constant for a given substance provided ____ and _____ are constant

Answer 19

proportional
- extinction coefficient

temperature, wavelength

Question 20

Absorbance is _____ to path length

Absorbance is ____ to concentration

Beer’s law is _____ dependent

• need to run a blank
• plotting calibration curve should give a slope of

Answer 20

proportional

proportional

concentration
- εb (molar absorptivity and )