Spectroscopy Flashcards by Nancy Chukwumezie

What are the 5 components of optical spectroscopy

Stable source of Radiant energy
Transparent container for sample
A device that isolates specific region of spectrum
Radiation detector
Signals processor and readout

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Draw the gerneral layout for an optical spectroscopic method based on ABSORPTION

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Draw the gerneral layout for an optical spectroscopic method based on FLUORESCENCE

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Draw the gerneral layout for an optical spectroscopic method based on EMISSION

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What are optical spectroscopic methods based on (total of 6)

Absorption
Fluorencence
Phosphorensence
Scattering
Emission
Chemilumenescence

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What is Spontaneous Emission?

When an atom spontaneously jumps into a state with lower energy via the emission of a photon

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What is Stimulated Emission?

When an atomic electron goes to a lower state after interracting with an elecromagnetic wave of a certain frequency via the emission pf a photon with the same phase, frequency, wavelength. etc..

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What is a photon?

a stream of discrete “particles” or “wave packets of energy”

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The energy of a photon is proprotional to the _________ of the radiation.

frequency

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What is the wave nature of a single frequency electromagnetic beam?

The electric field oscillates in a **plane perpendicular **to the magnetic field, in a plane-polarized wave.

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What happens to the electric field if radiation is unpolorized?

a component of the electric field would be seen in **all planes. **

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what is Planck’s constant (**h) **?

6.63 x 10^-34 J•s

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1 J = _____ ev (electron volts)

______ J = 6.24 x 10¹⁸ev

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What is the equation for frequency?

frequency= speed of light/ wavelength

v = c/λ

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What is the equation for **Energy? **

Energy = Planck’s constant • fequency

E=hv

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What is the equation to find refractive index?

Refractive index = (velocity in vaccum) **/ **(velocity in medium)

n_i= c/v_i

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What is dispersion?

The variation in refractive index of a substance with wavelength or frequency

(ie. when a wavelength changes, so does the refractive index.)

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What are the two types of regions in dispersion plots?

normal and anomalous dispersion region

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how does a normal dispersion region look on a dispersion plot?

there is a gradual increase in refactive index w/ increasing frequency (or decreasing wavelength)

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how does a anomalous dispersion region look on a dispersion plot?

there are sharp changes in the refractive index on the dispersion plot

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what is **black body radiation? **

The continous emission spectrum of a substance when heated to incandescence.

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Define **Relaxation. **

when an atom or molecule goes from excited state energy level to a lower energy level

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What is Stoke’s Shift?

the negative difference in frequencies of emitted radiation from the incident beam.

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The lowest state of a molecule is reffered to as _________.

ground state

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What is spectroscopy?

the study of the interraction of various types of radiation with matter.

concerning waves, what is a period?

The time in seconds required for a particle a medium to make one **complete** _vibrational cycle._

concerning waves, what is frequency?

The number of **vibrational cycles **per second

what is wavelength?

the distance between to maximas

what is the velocity of a wave dependent on?

The medium it's passing through

**Frequency** is the inverse of \_\_\_\_\_\_\_

**Period** is the inverse of \_\_\_\_\_\_

what is a vaccum?

the absence of a medium

**True or False?** excess energy can be released by heat.

**TRUE**

What is the name of this diagram?

**Jablanski Diagram**

what is the result of a jablanski diagram?

**A SPECTRUM**

what is the quantum theory?

atoms/moleules/ ions have limited number of discrete energy levels

Total Energy is the sum of \_\_\_\_\_\_\_\_\_\_

E_electronic + E_vibrational + E_rotational

What is non-raidative relaxation?

loss of energy in small steps

Which relaxes faster, Fluorescence or Phosphorescence?

Fluorescence.

How does **Stokes shift** occur?

When a certain energy is put in a sample, you should get **less** energy out therefore the wavelength should be longer

How does **Anti-Stokes shift** occur?

When you put in a certain amount of energy in a sample, and end up getting **MORE** energy out. therefore having a shorter wavelength. This can occur when **heat is added**

What are the four major categories of spectrochemical methods.

1. Emission 2. Luminescence 3. Scattering 4. Absorption \*all require radiant power, P \*

Equation of Transmittance?

**T = (P/P₀) x 100% **

What is the equation for **Absorbance?**

**A = -log₁₀T** **A = log(P₀/P)** **A = 2 - log₁₀%T** **A= εbc**

What is Beer's Law?

Absorbance = [molar absorbitivity L •mol^-1 •cm^-1] [path length cm] [concentration of analyte] **A= εbc**

Beer's law is _________ for mixtures at a given wavelength

**Additive **

What are the limitations to Beer's Law

* Only for dilute solutions * Monochromatic radiation * Path length must be the same \*\*high concentrated analyte makes it hard for absorption of radiation to happen\*\*

Draw the general layout for a **single beam** instrument

Draw the general layout for a double beam-in-space instrument

Draw the genral layout for a double-beam-in-time instrument

what is a **charged coupled device (CCD)**

is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated. integrated circuit etched onto a silicon surface forming light sensitive elements called pixels. Photons incident on this surface generate charge that can be read by electronics and turned into a digital copy of the light patterns falling on the device. like cellphone cameras

What is a **Charge injection Device (CID)**

A charge-transfer device used as an image sensor in which the image points are accessed by reference to their horizontal andvertical coordinates

Draw a general diagram of a photodiode array

What are the two types of wavelength selectors

1. Filters 2. Monochromators

What type of filters are there? Order from least best to best.

1. Absorption Filters (inefficent) 2. Interference filters (very effeicent) 3. Holograohic Notch Filter (best)

what does a monochromator consist of.

1. Entrance Slit 2. Collimating lens OR Mirror 3. Prism OR Grating to dispense radiation 4. Focusing element 5. Exit Slit

what does a **Photomultiplier Tube (PMT) **do?

Amplifies signals which allows for sensitive detection.

Photomultiplier tube is based on the \_\_\_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_ by _________ .

**Photoelectric effect; Einstein**

Define **electron cascade.**

propagation of electrons, build up of electrons.

What would be most likely used as optical source for wavelength of 200-400 nm and what type of Electromagnetic radiation is in that region?

* H₂ or D₂Lamp (moest likely deterium lamp) * UV

What would be most likely used as optical source for wavelength of 400-700 nm and what type of Electromagnetic radiation is in that region?

* a Tungsten Lamp * Visible light

what does laser stand for?

Light Amplification by stimulated emission of radiation

What are the four important prcoesses in laser action

1. Pumping 2. Spontaneous emission 3. Stimulated Emission 4. Absorption

what is pumping

excitation by electrircal, radiant, or chemical energy

What must happen in order for **light amplification** to occur?

the number of photons produced by stimulated emisssion must **exceed **the number lost by absorption. known as **popultion inversion** **(Ie. THERE IS MORE ENERGY IN THE EXCITED STATE THAN IN THE LOWER ENERGY STATES)**

Population inversions are created by \_\_\_\_\_\_\_.

**Pumping**

Define what happens to produce a Three-Level Laser system

The transition for a laser radiation is between an excited state and the ground state

Define what happens to produce a Four-Level Laser system

there is an additonal excited state between the most excited state and ground state

What is the advantage of a four level laser system?

population inversions are achieved more easily, which is essential laser action

Repilca gratings are manufactured from a \_\_\_\_\_\_\_ _ ._

**master grating**

what is the equation for constructive interference?

diffrection order•wavelength =distance betweenn reflective sufaces( sin Ө₁+ sin Ө₂) **nλ = d(sin i + sin r)**

What is the **effective bandwidth** of a filter

one half the bandwidth when the two slit widths are identical

what does a PMT consist of?

* photocathode * Dynodes * Anode * Amplified Current \*\*in a vaccum tube\*\*

Draw the basic structure of a PMT

What does a photocathode do?

Converts light (photons) into an electron current

What does a dynode do?

dynodes serve as an electron multiplier

what does an anode do?

delivers an output signal

1 Å = \_\_\_\_\_cm

\_\_\_\_\_Å = 10^-8cm

1 m = \_\_\_\_\_nm

\_\_\_\_m = 10⁹ nm

10 Å = ____ nm

\_\_\_\_\_Å = 1 nm

1 MHz = \_\_\_\_\_\_Hz

\_\_\_\_\_\_MHz = 10⁶Hz

1 mol = \_\_\_\_\_\_photons

\_\_\_\_ mol = 6.02 x10²³ photons

1 m = ______ µm

\_\_\_\_\_ m = 10⁶ µm

what is coherent radiation?

the phases of two waves that represent radiation differ by a known constant.

what is the work function of a substance?

the energy required to remove an electron from the surface of a substance

Define Photoelectric effect.

The energy contained inn a wave and particles depends on the frequency and intensity

what is the equation used to find refractive index when given angles

refractive index = **(**angle of incidence of "x"**)** **/ (**angle of refraction of "x"**)** n_x= sin Ө_i_x**/ **sin Өrx

Equation to calculate concentrations in two unknown solutions

A₁= (ε_m1•b•c_m) + (ε_n1•b•c_n) A₂= (ε_m2•b•c_m) + (ε_n2•b•c_n)

Equation to calculate the new concentration of a sample

C_x = (A₁•C_s•V_s) **÷ **(A₂- A₁)V_x

why are holographic notch filters the best?

they provide a much narrower bandwidth and higher intensities

absorption flters are mainly used for what region?

visible regions

what is a disadvantage of using abosption filters?

they often block a significant portion of desired radiation

what is the range on a spectrum where visible light seen? (in nm)

400-700nm

Which source of energy is good for wavelengths from 160-380 nm

H₂and D₂Lamp

Which source of energy is good for wavelengths from 320-2400 nm?

tungsten lamp

Which source of energy is good for wavelengths from 200-1000nm

Xe arc Lamp

Which source of energy is good for wavelengths from 0.4-20 µm ?

nernst glower

Which source of energy is good for a line source of UV/Visible?

hollow cathode lamp

Which source of energy is good for a line source of UV/Visible/IR?

Lasers

\_\_\_\_\_\_\_\_\_\_ grating consists of ~300 blazes/min

Echelle

\_\_\_\_\_\_\_\_\_\_grating consists of ~1300 blazes/min

echellete

What are the units for reciprocal linear dispersion?

**nm/mm** **OR** **Å/mm**