Test 3 Flashcards
time spectrum vs space spectrum
both can be described by a frequency which corresponds to a wavelength of photons, and a specific amplitude also correlated to that wavelength. difference: time is expressed as a function of time, space uses a function of retardation as a measure of space, and time domain can be described by a higher frequency and therefore shorter tau than space domain
time domain vs frequency domain
can encode non electrical domain information (like number), belong to electrical domains and the time domain. differences: intensity as a function of time vs intensity as a function of frequency. and freq domain can be gotten from dispersive spectrometry but time cannot
inferogram time frequency for michelson interferometer (xray)
2(vm)/lambda aka 2(vm)v/c where vm is velocity of mirror
what does michelson inferometer measure directly in spectrophotometry
space measurement
retardation =
(delta) = 2(mirror drive distance)
tau
time for a freq (= 1/f)
delta and wavenumber in FTIR
every delta in space spectrum contains info for every wavenumber and vice versa
fourier transformation
info goes from space domain to frequency domain
resolution for FTIR eq
improves with inverse delta
overtones
first overtone = 2 and so on, just multiply eq by that number because we’re fools
time domain graph
x axis has time, with 0 at the center
FTIR advantages
high S/N (very fast), accurate, precise, source reaches detector in one pulse, “high throughput” (fast)
IR applications
qualitative distinction of functional groups and id of molecules, quantitative things like BAC and conc similarly based on intensity of peaks
Raman scattering
inelastic. has a delta E bc delta E = h(v1 - v2) and v1 and v2 are not equal due to vibration. Has antistokes and stokes lines at specific distance from the rayleigh line for specific species. polarizability (alpha) changes because distance btwn molecules changes.
Compton scattering
longer wavelengths due to energy lost in ionization (as opposed to vibration)
photoionization
adding radiation to species to induce ionization
Rayleigh scattering
the vast majority of scattering. elastic, v1 = v2
remember wavelength to freq conversion
c = v(lamba)
boltzmann eq
ratio of excited:ground state = e^(-deltaE/kT), T must be in K
Raman vs IR
based on polarizability vs change in dipole, quadratic eqs on character table vs translational symbols, IR has transition to eigenstate while raman goes to a virtual state. both measure light and matter interaction and molecular vibrations. the interactions differ (vibration vs scattering), IR transition is from ground to some excitation while Raman is from virtual state to ground.
stokes and anti-stokes magnitude
stokes have much larger magnitude than anti-stokes, the ratio is temp-dependent (Boltzmann eq) and magnitude is also based on the power of the excitation radiation
typical raman spectrum lines
only stokes lines usually
Raman wavelengths overlap with other processes
far from absorbance but often stokes overlap with fluorescence
Raman intensity eq
varies with source freq^4, also varies with concentration
raman original experiment setup
sun, lenses, blue-violet filter, sample, yellow-green filter, observer (at 90 degrees)
Raman equipment setup
laser source, sample, selector, detector (can be 180 or 90 degrees). usually HeNe laser
minimizing fluorescence interference with Raman
use FT instrument
FTIR vs FTRaman spec
both use michelson inferometer and give qualitative info on functional groups, energy for Raman is Excitation - deltaV where IR is just the delta V, and setup for Raman is more complex than IR also Raman sample is at 90 while IR is at 180
Raman advantages over IR for quantitation
water interferes with it less, machines are more compact for field work
Raman intensity eq
Ir = kv(Iex)C - slope, varies with excitation intensity
polarizability for Raman to be scattering produced
alpha varies based on r (distance btwn atoms)
temp change of stokes vs antistokes
stokes - heating, anti-stokes = cooling (vibrations need to release or get energy somehow)
lasers for Raman
HeNe is less likely to produce fluorescence than Ar or Kr (these are higher energy), diode lasers are better than elemental to have high power with low interference from fluorescence. near-IR (Nd:YAG) used for FTRaman, high power again but cannot make e- transitions happen
lifetime of virtual state/Raman
1x10^-15 seconds
SERS
surface enhanced Raman spec. detects for molecules adsorbed to a surface, can be as sensitive as fluorescence due to enhancement of the EM waves by the metal.
atomic spectroscopy applications
lead detection, shifting of celestial bodies based on composition and red shift
the sun emits..
black body radiation
transition rules**
delta S = 0, delta L = 0 or +-1, delta I = +-1, delta J = 0 or +-1 (most of these are angular momentum), spin is S
singlet excited state
e- are in diff levels but still have opposite spins
triplet state value
is +- 1 until change occurs bc split could be resolved by move of either e- in the system (diff levels, same spin)
why cant triplet be in ground state
pauli exclusion principle - no same spins in 1 orbital
how is atomic spectra generated (atom)
outermost e- specifically homo-lumo gap unique to each element
thermal excitation
spark, heat (non radiative energy) can be added causing excitation and emission of radiation. this is why elements have spec colors in flame
boltzmann eq for atomic spectra
excited/ground = (Pj/Po) e^(-deltaE/kT) where P are number of electrons that go in higher energy over the lower energy orbital
why is atomic line width so thin
no vibrations to interfere
atomic line is broadened by…
uncertainty, doppler effect, high pressure, electrical and magnetic fields
heisenberg uncertainty energy and time eq
delta v * delta t greater than or = 1
delta t in atomic spec
lifetime of the excited state
derived eq for heisenberg uncertainty calc
delta lamba = lamba^2*deltav/c
think about derivatives. c/x
-c/x^2
doppler effect and eq
wavelength inc as object moves away, dec as it approaches. observed freq = (c + observer v)/(c+source v) (actual freq)
doppler broadens atomic lines eq
due to deviation in wavelength. change/initial = v/c where v is relative velocity of object
thermal doppler broadening calculation
maxwell distribution (we dont do this)
high pressure broadening why
more atomic collisions
stark effect
electric field broadening
zeeman effect
magnetic field broadening (due to e- energy levels splitting)
temp and atomic spectra
as shown in boltzmann eq, it excites. so constant temp is important for these measurements.
UV vs IR
UV has noise in the radiation source, IR has it in the detector
resolution for inferometer
delta wavenumber = 1/delta
1 angstrom
0.1 nm
why is emission effected by temp change more than fluor or absorbance
the pop measured is excited state where for the others it is ground state, temp changes the fraction that are excited which really impacts emission but it is still a tiny proportion compared to ground for fluor and abs.
three types of atomic spectroscopy
emission, fluorescence, absorbance
atomization
sample is turned into atomic vapor, very crucial for error (causes the error in the process for the most part)
continuous vs discrete atomizers
continuous is often nebulizer feeding soln into plasma or flame= steady population of excited atoms, while discrete is a specific amt of sample in chamber being atomized, such as electrothermal atomizer
higher temperature in atomization can cause..
more ions in sample
flame atomization
used for atomic spec of gases, sample is misted to the flame, and this yields atoms, molecules and ions
flame hot zone
above the primary combustion zone
highest temperature atomization method
electric spark (40000)
glow discharge device
introduces and atomizes sample. low voltage is applied to argon in chamber with cathode coated in sample, these molecules are sputtered and some are excited, leading to glow (sample emission).
electrothermal atomizers
milliseconds, high temp 2000-3000. temp increases from low for evaporation, ashing, and then inc. of current rises temp rapidly to atomize
plasma
electrically conducting gas phase with lots of cations and e-, up to 10000 K
types of plasma sources
ICP (inductively coupled), microwave induced, direct current
getting atomization from solid sample
high voltage electric spark
electrodeless discharge lamp sources
magnitudes more intense lines than hollow cathode, but need different lamp for each element
two line correction method
source reference line close to analyte line but not absorbed by analyte, should be constant to correct for matrix interference
continuum source background correction
deuterium and hollow cathode lamps alternate, deuterium giving background noise and hc the total signal, the computer subtracts these.
Zeeman effect correction
atomic lines split by tiny portion of nm due to magnetic field splitting, this can be used to combat background interference. source can be split.
chemical interference
formation of compounds of low volatility, ionization, dissociation during the atomization process. leads to diff analyte properties.
combating compounds of low volatility
releasing agents or high temps
internal standard
adding same amount of another species to each standard addition sample that contains sample, this will also have a response we can measure, and the ratio of unknown/internal standard will be constant to combat fluctuations
calcs with internal standard
ratio of unknown/standard is the signal
x-ray source range
0.1-25 A
types of x-ray spectroscopy
fluorescence, absorbance, diffraction, photoelectron spectroscopy
eq for thickness of sample in x-ray
ln(Po/P)=mu(x) where mu is linear abs. coefficient and x is thickness, OR ln(Po/P)=mu(density)x where mu is “mass absorption coefficient” (cm^2/g)
bragg’s law
for x ray diffraction scattered rays. n(lambda)=2dsin(theta) where d is distance btwn atomic layers
karat
purity measure (gold), 24 = 100%
carat
weight measure (diamonds), 1C=200mg
Geissler
discovers x-ray with his tube
1st picture
using x-ray, roentgens wife’s hand
Siegbahn
relates x ray to atomic structure > boom, analysis
Siegbahn notation
shows how e- jump btwn orbitals = K and L series for p and d orbitals
x-ray instrumentation steps
source, selector (can be crystal diffraction), sample, detector, processor and readout
x-ray sources
tubes, secondary fluorescent x-rays, radioisotopes, synchotron radiation
cyclotron sources
EM radiation can be generated when charged particles are accelerated radially = synchotron radiation (ie CERN)
short wavelength limit (eq)/duane-hunt law
Ve = hc/lambda, so lambda (in A) = 12,398/voltage
x-ray detector types
gas-filled transducer, scintillation counters, semiconductors, film
scintillation detector
NaI crystal (often) fluoresces when hit with radiation from sample. pmt counts the light
semiconductor x ray detector
energy dispersive, multiple layers to disturb e- and carry signal to amplifyer
calculating mass absorption coefficient for a compound
%element*mass abs coefficient
releasing agent
cations that bond to atoms that would otherwise form non-volatile complexes with the analyte, preventing analysis
protective agents
form volatile compounds with the analyte so it can be measured in spite of the presence of other spp
ionization suppressors
reduce ionization by providing a source of e- so the species will go back to elemental form
hollow-cathode lamp
most common AAS source. light is produced by metal atoms that have been excited by inert gas from electrical stimulation
sputtering
process within hollow cathode lamp where the metal produces an atomic cloud
self-absorption
process in hollow-cathode lamp where unexcited sputtered atoms absorb the radiation from excited atoms (this radiation is now not reaching the sample)
spectral interference
very close interference that cannot be resolved with the peak of the analyte
radiation buffer
when some of an interfering substance is present, this is adding a bunch of it so that the presence of that small interference becomes insignificant. This measurement can be controlled for.
solute-volatilization interference
changes in solute volatility based on presence or absence of another species.
source modulation
the source output is modulated periodically (ie with a chopper) to eliminate interference from the portion of the flame light that is at the same wavelength as the result we want to measure
plasma advantages over flame
high temp, versatile for many elements at just 1 temp setting while flame must be adjusted, works for very low conc of compounds that can take high heat and form refractory compounds, and works for nonmetals, also doesnt ionize much bc of the e- in the plasma
arc vs spark spectra
arc is low temp (4000) and has atomic lines, spark is very high (40000) and has ionic lines
sequential vs simultaneous multichannel
sequential can only measure 1 sample accurately in short time, must do one at a time, simultaneous takes that amt of time to do many many samples.
energy dispersive x-ray fluorescence spectroscopy
uses multi-channel detector, measures radiation of diff spp using monochromator (DCC) before sample. worse resolution than WD.
wavelength dispersive x-ray fluorescence spectroscopy
has 2 DCCs (before and after sample), focuses to spec wavelength. leads to higher resolution
DCC
doubly curved crystal, monochromator for x-ray spec
applications of ED-XRF and WD-XRF
ED for things in space bc it is more compact and the readings are still workable, WD for biological detection bc it works so well
hkl in problems
given as peak XXX (hkl)
extended x-ray absorption fine structure
tells configuration of atoms
x-ray absorption near edge structure
probes oxidation state (valence)
gas filled transducer
x-ray detection method where when gas is ionized by x-rays it conducts`
semiconductor x ray detectors
are electric. can use CCD (charge coupled) or lithium-drifted silicon
eq for lattice edge length
d = a/sqrt(h^2+k^2+l^2). a is lattice constant = cube edge length
natural width of atomic emission line
10^-5 nm (only due to uncertainty principle)
excitation for as
for flour it is wavelength, for AES it is thermal
k and l emission lines
When an electron beam source collides with atoms in a sample, the incoming electron is decelerated and X-ray
energy is produced. Only atomic number atoms larger than 23 produce K and L emission lines; smaller ones
produce only the K series. K series spectral lines are produced when the high-energy electrons from the
cathode remove electrons from those orbitals nearest the nucleus of the target atom. As the outer orbital
electrons relax to replace the missing electron, X-ray radiation is given off. L series lines come when the
electron initially lost is from the second principal quantum level orbital.
working with mass coefficients for x ray
can add them to use the weight fraction of a molecule ie double it for % of N2, calculate u for a solvent like ethanol by adding the weight % and u of each (meta-math)
atomic emission vs atomic fluor
Similarities: Both use wavelength selectors after sample; line widths from broadening effects; quantitatively determine elemental intensity; photon generated during excited -> ground state transition
AES: ICP/flame/etc. thermally excites the sample; more popular than AFS
AFS: wavelength source for excitation; smaller useful concentration range, but for some elements like Hg lower LODs can be determined; measured at 90° from source path; for environmental samples; lamp sources
for x ray crystal edge questions
dont forget it’s VOLUME!!
