specto

SPECTROSCOPY

Interaction of Radiation with a sample

SPECTROSCOPY

The study of molecular or atomic structure of a substance by observation of its interaction with electromagnetic radiation

QUANTITATIVELY

For determining the amount of material in a sample

QUALITATIVELY

For identifying the chemical structure of a sample

SPECTROMETRY

Defined as method of analysis which deals with the measurement of spectra.

SPECTROMETRY

the measurement of the interactions between light and matter, and the reactions and measurements of radiation intensity and wavelength.

Spectra

- reflected, scattered, absorbed, fluoresce and cause photochemical reaction like bond breaking

Spectrophotometry

is a branch of spectrometry which embraces the measurement of the absorption by chemical species of radiant energy of definite and narrow wavelength approximating monochromatic radiation.

Colorimetry

is a branch of spectrophotometry in which the absorption measurement is made in thevisible region of the spectrum

Electromagnetic spectrum

is the term to define the complete system of energy propagated in wave form

Electromagnetic spectrum

Energy in this nature is referred to as radiant energy and appears in such apparently different forms as sunlight, color, radiowaves, etc.

Radiant energy

refers to energy in the uv, visible, and ir regions of the electromagnetic spectrum.

X-Ray, γ Rays,

ex. High energy sources produce breaking of bonds

UV / VISIBLE Spectroscopy

ex. Medium energy sources excite electrons

Infrared Energy

ex. Low energy sources produce vibrations in chemical bonds

Microwaves and Radio waves

ex. Very low energy sources produce rotation of the chemical bonds

Light

electromagnetic radiation within a certain portion of the electromagnetic spectrum.

Light

The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight.

wavelength

The length of a complete wave or cycle from peak of wave to the peak of the next is called

Wavenumber

number of waves per centimeter, equivalent to 1/wavelength(cm)

FREQUENCY

complete cycle which pass a given point per second

micrometer, nanometer, angstrom

units of wavelength

cps/ hertz

units of frequency

1cps

1 hertz =

200 - 380 nm

380 - 780 nm

780 - 3000 nm

3.0 - 15 um

15 - 300 um

The ranges of the wavelength of radiant the practice of radiation of single energy of importance in spectrophotometry are:

UV =

Visible =

Near IR =

Medium =

Far IR =

Monochromatic radiation

radiation of single wavelength

Group Frequency Region

The region from 3 to 8 um, because the absorption peaks which appear in this region are due to functional groups formed in the organic compounds.

Fingerprint Region

The region from 8 to 15 um because this region gives a spectrum of the molecule as a whole.

Monochromatic radiation

is obtained by using prism or diffraction grating.

VISIBLE SPECTROSCOPY

Absorbance and reflectance

COMPLEMENTARY

When a sample only absorbs light of a single wavelength the eye sees __ colours.

WHITE

If the material completely REFLECTS all light it appears

GREY.

If the material absorbs a constant fraction of the light across the spectrum it appears

BLACK

If the material completely ABSORBS all the light it appears

Chromophore

functional group which absorbs radiant energy in the uv or vis regions

Colorimetry

branch of spectrophotometry in which absorption takes place in the vis region

concentration

Intensity of the transmitted radiant energy is a function of the__

transverse wave

Light transmitted is in the form of __at an enormous velocity

give the symbol of the ff:

1. Velocity of Radiation (constant in vacuum)

2. Wave Length, the distance between successive maxima or minima of a wave, measured in cm, µm (10-4 cm) , nm (10-7 cm) and Å (10-8cm)

3. Frequency of Radiation (cycles/sec), is the number of oscillation of the field per second, Hz or cps

Amplitude

is the distance of half height of the wave Wavenumber (ṽ)

Amplitude

is the number of waves per centimeter and is equal to 1/wavelength (cm).

photons orquanta.

Radiant energy absorbed is in the form of discrete parcels of energy known as

energy E

The __ of photon depends upon the frequency of the radiation

constant

Velocity of all forms is

frequency and wavelength

Differences lie in the

Absorbed energy

Molecule absorbs energy that requires to elevate to higher level

Initial energy state

- ground state to higher energy state

Electronic (UV)

Associated with the overall motion of electrons around the nuclei

Vibrational(IR)

Associated with the motion of atoms within the molecule

Rotational(Microwave)

Associated with the overall rotation of the molecule

Translational (notquantized)

Associated with the motion of the molecule as a whole

E electronic + E vibrational + E rotational

Total potential energy =

Electronic transitions

Involves the transfer of electrons between different electronic state ground state to the excited state

Electronic transitions

When UV is absorbed an electron is raised from the ground state to excited state, loses its vibrational energy, decays to ground state, emitting UV or visible light flourescence

phosphorescence.

When the transition back to the ground state is delayed it results to

Group frequency region of 3.0 to 8.0 µm, wave number of 4000-1300cm-1

Fingerprint region 8.0 to 15.0 µm, wave number of 1300 - 400cm-1

Two general regions under IR

IR radiation

causes the vibrations of covalent bonds within that molecule. These vibrations include the stretching and bending modes

Stretching

- distance bet two atoms increases or decreases

Symmetrical and Asymmetrical

2 types of stretching

Bending

- position of the atom changes relative to the original bondaxis

Bending

deformation

In-Plane

Out-of Plane

2 types of bending

In-Plane

scissoring and rocking

Out-of Plane

wagging and twisting

Bending vibrations

generally require less energy and take place at longer wavelength than the corresponding stretching vibrations

Beer' s Law

states that the power of a transmitted radiant beam decreases exponentially as the concentration of the solution containing the absorbing chemical species increases arithmetically.

Absorbance

is directly proportional to concentration

Bouguer ' s Law

states that the power of a transmitted radiant beam decreases exponentially as the thickness of the solution containing the absorbing chemical species increases arithmetically

Beer-Lambert law

this is example of what law:

green laser light in a solution of Rhodamine B6

Beer - Lambert or

Beer - Bouguer' s Law

is a combination of the above law and relates the power of the incident and the transmitted radiant beam to the thickness and concentration of the solution containing the absorbing chemical species.

Transmittance

The ratio of the radiant power transmitted by the solution to the radiant power transmitted by the blank (solvent).

Transmittance

Defined as the ratio of the intensity of light emerging from the solution (I) to that of incident light entering (Io)

Absorbance

Also called optical density, absorbancy, extinction coefficient

Concentration

Expressed in grams of solute per liter of solution.

Absorptivity

The value obtained by dividing the absorbance (A) by the product of concentration, expressed in grams per liter, and the path length, expressed in centimeters

Molar Absorptivity

The value obtained by dividing the absorbance (A) by the product of concentration of the solution, expressed in moles per liter, and the path length, expressed in centimters

Absorption Spectrum

The graph obtained when absorbance or any function of absorbance is plotted against wavelength.

Spectrophotometer

These instruments may either be manually operated or automatic recording instruments.

Cuvette

small tube of circular or square cross section, sealed at one end, made of plastic, glass or fused quarts ( UV lights)designedto hold a sample

456 - 705 nm

Glass cuvette sample limit -

380 - 780 nm

Plastic cuvette sample limit -

below 380 nm

Fused quarts cuvette sample limit

Beckman DU-2 spectrophotometer.

An example of a null-balance manually operated instrument 5i0s the

Beckman DU-2 spectrophotometer

This instrument which covers the UV, visible and near IR regions has continuous range from 190-1000 nm isolating spectra region from 0.5 - 1.5 nm.

Bausch and Lomb Spectronic 20.

An of a direct-reading manually example operated sp51ectrophotometer is the

Bausch and Lomb Spectronic 20.

This instrument has an operating range of 240 - 950 nm

SA curve

spectral absorbance curve, plot of absorbance values against wavelength

Beer's plot

plot of absorbance values against a series of known solute concentration