Chapter 17 - Fundamental to Spectroscopy Flashcards
Electromagnetic radiation (light) has ____ like properties and ________ like properties
Wave-Particle Duality
wave, particle
some properties of light are best described by as a wave while others as a particle
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
amplitude and wavelength
wavelength
amplitude
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 ______ _______
frequency
frequency
inversely related
As wavelength decrease, energy and frequency ______
As wavelength increases, energy and frequency _____
increase
decrease
something is quantized if it can have only particle values
Energy is ____ to frequency
Quantization
proportional
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 _________
ground state
- excited state
lowered back down to ground state
- 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 ______
electron transition
a. singlet state
b. triplet state
_____ 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
infrared and microwave
- vibrational, rotational
vibrational, rotational
What happens to absorbed energy?:
After absorption to ____ to ____, _____ ______ is the first thing occur first
S0 to S1, vibrational relaxation
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 _____
a. S1
b. emits, S0, fluorescence
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 ______
interval conversion, S1
T1, intersystem crossing
- phosphorescence
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)
absorption
vibrational relaxation
- nonradiative decay
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
internal conversion
- radiation-less radiative
- heat
intersystem crossing
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
phosphorescence
- nonzero
- takes much longer
fluorescence
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 ________
spectrophotometer
irradiated
- irradiance
monochromatic
transmittance
absorbance
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 ___%
Transmittance (T)
Absorbance (A)
0
- 0 to 100
The color we see is _____ and colors we don’t see ____
molecule responsible for light absorption is called
transmitted, absorbed
chromophore
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.
Beer-Lambert Law
A (Absorbance)
ε (molar absorbitvity)
L (path length)
C (concentration)
Absorbance is ______ to molar absorptivity
- called the _____ coefficient
It is a constant for a given substance provided ____ and _____ are constant
proportional
- extinction coefficient
temperature, wavelength
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
proportional
proportional
concentration
- εb (molar absorptivity and )
