UNIT4 Spectroscopy (edit!) Flashcards
What is spectroscopy?
Interactions of readiation and matter
How is spectroscopic analysis measured?
Amount of radiatio produced or absorbed
What waves are used?
γ-ray, X-ray, ultraviolet (UV), visible, infrared (IR), microwave, and radio-frequency (RF)
ALSO acoustic, massm electron spectroscopy
What is the most widely used method?
elucidation of molecular structure and quantitative and qualitative determination
What is electromagnetic radiation?
Wave with properties of a wavelength, frequency, velocity and amplitude
What medium of transport does electromagnetic radiation use?
No medium
How can electromagnetic radiation be seen?
discrete packets of energy paticles —> photons or quanta
What is the energy of the photon?
Proportional to its frequency
How is electromagnetic radiation modeled?
Waves consisting of perpendicularly oscillating electric and magnetic feild
Amplitude
Strength at a maximum in a wave
Period (p)
time in seconds for successive maxima and minima to pass a point in space
Frequency v
number of oscillations that occur in one second –> 1/p
What is the unit of frequency?
Hertz (Hz)
One cycle per second
What is the wavelength?
Linear distance between sucessive maxima or minima
Velocity
speed that depends on the medium and frequency
Is the frequency or velocity constant?
Frequency
What is wave number
Way to describe electromagntic radiation –> number of waves per centimeter = 1/λ
What is a photon?
Particle of electromagnetic radiation having zero mass and an energy of hv
What is the equation for wavenumber?
E=hv=hc/λ=hcv~
What is plank’s constant?
6.63*10^-34J
What are the most important interactions in spectroscopy
transitions between different E levels
Visible light spectrum
380-780
What is visible spectrum
180-380nm
What is another word to spectrochemical methods?
OPtical methods, even when you cannot see some of them
How do you begin a spectroscopic method?
Sample is stimulated by applying energy (heat, electirc, light, particles
What is the state of the analyte before the stimulus?
Lowest- energy / ground state
Why is the analyte in the ground state?
In order to transition to a higher more excited state
How do we acquire information about the analyte?
Measure the electromagnetic readiation emitted or the amount of electromagnetic readiation absorbed
The results of spectroscopy is expressed by…
Graphically by a spectrum –> plot of emitted/absorbed radiation as a function of frequency, wavelength or wavenumber
Emission spectroscopy?
Methods which the stimulus is heat or electrical
Chemiluminescence spectroscopy?
Excitation of analyte by chemical reaction
Absorption spectroscopy
light absorbed as a function of wavelength
photoluminesence spectroscopy
emission of photon measured following absorption
What are the most important forms of photoluminescence?
Fluorensence and phosphorescence
Every molecule is able of absorbing….
its own characteristic frequencies of elec radiation
What is the process of absorption of radiation?
Transfer energy to the molecule and results in a decrease in intensity of incident
What happens to the beam in absorption of radiation?
Attenuates the beam in accordance to the Beer-Lambert Law
What is Beer’s Law
Amount of attenuation depends on the concentration of absorbing moleules and the path length
According to Beer’s Law, the longer the length of the medium?
The greater attenuation
According to Beer’s Law, the higher the concentration of absorbers
The stronger the attenuation
What is the transmittance
the fraction of incident radiation transmitted by the solution
T=P/P0
Absorbance as a solution is denoted as
A=-logT=-log%T+log100=2-log%t
What happens with radiation at the cell wall
Reflection and scattering losses
–> can be substantial
How do we compensate for the scattering losses?
Reagent blank
What is absorbance according to Beer’s Law?
Absorbance is directly proportional t the concentration of the absorbing species c and to the path length c
A=Ebc
E–> absorptivity in L mol^-1 cm^-1
Why are high molar absorptivities good?
high analytical sensitivity
The longer the path length, the _____ the attenuation
Greater
As absorbance increases, transmittance ____
decreases
The study of the interaction between electromagnetic radiation and matter is…
Spectroscopy
Electromagnetic radiation is modeled as a ____ to explain different phenomena such as reflection, refraction, interference and diffraction
wave
When an excited chemical molecule returns to its ground state it ___ energy
emits
A plot of the emitted or absorbed radiation as a function of frequency, wavelength or wavenumber is ____
Spectrum
Beer’s law relates the __ of the electromagnetic beam to the path length and the concentration of absorbing species
attenuation
True or false: the attenuation of the electromagnetic beam results only from molecules absorbing electromagnetic energy
False
Vibration of chemical bounds is induced by ___
Infrared light
True or false: IR radiation causes transitions in the electronic, vibrational and rotational states.
False. Only in the rotational and vibrational states
Total energy in atomic and molecular absorption is a sum of what energies?
electronic, vibrational and rotational
What do the spectra of liquid, gas, nonpolar and polar states look like?
gas: many peaks resulting from transitions
liquid & non polar solvents: no fine structure, plus still peaks
polar solvents: band becomes blurred
Why do polar solvent have a blurred spectrum?
Because collisions between particles tend to spread energies of quantum states and the spectrum appears as a single broad peak
Beer’s law only applies to what type of solutions?
Dilute
Name some instrumental deviations to Beer’s law?
- Measurements must be made with monochromatic source radiation
- Polychromatic sources must be used with a filter to isolate band
- Stray radiation/light: result of scattering and reflection
- mismatched cells (intercept k will appear in calibration curve)
Name a chemical deviation to Beer’s Law
Absorbing species dissociates, associates or reacts with solvent to give a product that absorbs differently
