Test 3 Flashcards
(128 cards)
1
Q
time spectrum vs space spectrum
A
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
2
Q
time domain vs frequency domain
A
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
3
Q
inferogram time frequency for michelson interferometer (xray)
A
2(vm)/lambda aka 2(vm)v/c where vm is velocity of mirror
4
Q
what does michelson inferometer measure directly in spectrophotometry
A
space measurement
5
Q
retardation =
A
(delta) = 2(mirror drive distance)
6
Q
tau
A
time for a freq (= 1/f)
7
Q
delta and wavenumber in FTIR
A
every delta in space spectrum contains info for every wavenumber and vice versa
8
Q
fourier transformation
A
info goes from space domain to frequency domain
9
Q
resolution for FTIR eq
A
improves with inverse delta
10
Q
overtones
A
first overtone = 2 and so on, just multiply eq by that number because we’re fools
11
Q
time domain graph
A
x axis has time, with 0 at the center
12
Q
FTIR advantages
A
high S/N (very fast), accurate, precise, source reaches detector in one pulse, “high throughput” (fast)
13
Q
IR applications
A
qualitative distinction of functional groups and id of molecules, quantitative things like BAC and conc similarly based on intensity of peaks
14
Q
Raman scattering
A
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.
15
Q
Compton scattering
A
longer wavelengths due to energy lost in ionization (as opposed to vibration)
16
Q
photoionization
A
adding radiation to species to induce ionization
17
Q
Rayleigh scattering
A
the vast majority of scattering. elastic, v1 = v2
18
Q
remember wavelength to freq conversion
A
c = v(lamba)
19
Q
boltzmann eq
A
ratio of excited:ground state = e^(-deltaE/kT), T must be in K
20
Q
Raman vs IR
A
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.
21
Q
stokes and anti-stokes magnitude
A
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
22
Q
typical raman spectrum lines
A
only stokes lines usually
23
Q
Raman wavelengths overlap with other processes
A
far from absorbance but often stokes overlap with fluorescence
24
Q
Raman intensity eq
A
varies with source freq^4, also varies with concentration
25
raman original experiment setup
sun, lenses, blue-violet filter, sample, yellow-green filter, observer (at 90 degrees)
26
Raman equipment setup
laser source, sample, selector, detector (can be 180 or 90 degrees). usually HeNe laser
27
minimizing fluorescence interference with Raman
use FT instrument
28
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
29
Raman advantages over IR for quantitation
water interferes with it less, machines are more compact for field work
30
Raman intensity eq
Ir = kv(Iex)C - slope, varies with excitation intensity
31
polarizability for Raman to be scattering produced
alpha varies based on r (distance btwn atoms)
32
temp change of stokes vs antistokes
stokes - heating, anti-stokes = cooling (vibrations need to release or get energy somehow)
33
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
34
lifetime of virtual state/Raman
1x10^-15 seconds
35
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.
36
atomic spectroscopy applications
lead detection, shifting of celestial bodies based on composition and red shift
37
the sun emits..
black body radiation
38
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
39
singlet excited state
e- are in diff levels but still have opposite spins
40
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)
41
why cant triplet be in ground state
pauli exclusion principle - no same spins in 1 orbital
42
how is atomic spectra generated (atom)
outermost e- specifically homo-lumo gap unique to each element
43
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
44
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
45
why is atomic line width so thin
no vibrations to interfere
46
atomic line is broadened by...
uncertainty, doppler effect, high pressure, electrical and magnetic fields
47
heisenberg uncertainty energy and time eq
delta v * delta t greater than or = 1
48
delta t in atomic spec
lifetime of the excited state
49
derived eq for heisenberg uncertainty calc
delta lamba = lamba^2*deltav/c
50
think about derivatives. c/x
-c/x^2
51
doppler effect and eq
wavelength inc as object moves away, dec as it approaches. observed freq = (c + observer v)/(c+source v) (actual freq)
52
doppler broadens atomic lines eq
due to deviation in wavelength. change/initial = v/c where v is relative velocity of object
53
thermal doppler broadening calculation
maxwell distribution (we dont do this)
54
high pressure broadening why
more atomic collisions
55
stark effect
electric field broadening
56
zeeman effect
magnetic field broadening (due to e- energy levels splitting)
57
temp and atomic spectra
as shown in boltzmann eq, it excites. so constant temp is important for these measurements.
58
UV vs IR
UV has noise in the radiation source, IR has it in the detector
59
resolution for inferometer
delta wavenumber = 1/delta
60
1 angstrom
0.1 nm
61
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.
62
three types of atomic spectroscopy
emission, fluorescence, absorbance
63
atomization
sample is turned into atomic vapor, very crucial for error (causes the error in the process for the most part)
64
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
65
higher temperature in atomization can cause..
more ions in sample
66
flame atomization
used for atomic spec of gases, sample is misted to the flame, and this yields atoms, molecules and ions
67
flame hot zone
above the primary combustion zone
68
highest temperature atomization method
electric spark (40000)
69
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).
70
electrothermal atomizers
milliseconds, high temp 2000-3000. temp increases from low for evaporation, ashing, and then inc. of current rises temp rapidly to atomize
71
plasma
electrically conducting gas phase with lots of cations and e-, up to 10000 K
72
types of plasma sources
ICP (inductively coupled), microwave induced, direct current
73
getting atomization from solid sample
high voltage electric spark
74
electrodeless discharge lamp sources
magnitudes more intense lines than hollow cathode, but need different lamp for each element
75
two line correction method
source reference line close to analyte line but not absorbed by analyte, should be constant to correct for matrix interference
76
continuum source background correction
deuterium and hollow cathode lamps alternate, deuterium giving background noise and hc the total signal, the computer subtracts these.
77
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.
78
chemical interference
formation of compounds of low volatility, ionization, dissociation during the atomization process. leads to diff analyte properties.
79
combating compounds of low volatility
releasing agents or high temps
80
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
81
calcs with internal standard
ratio of unknown/standard is the signal
82
x-ray source range
0.1-25 A
83
types of x-ray spectroscopy
fluorescence, absorbance, diffraction, photoelectron spectroscopy
84
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)
85
bragg's law
for x ray diffraction scattered rays. n(lambda)=2dsin(theta) where d is distance btwn atomic layers
86
karat
purity measure (gold), 24 = 100%
87
carat
weight measure (diamonds), 1C=200mg
88
Geissler
discovers x-ray with his tube
89
1st picture
using x-ray, roentgens wife's hand
90
Siegbahn
relates x ray to atomic structure > boom, analysis
91
Siegbahn notation
shows how e- jump btwn orbitals = K and L series for p and d orbitals
92
x-ray instrumentation steps
source, selector (can be crystal diffraction), sample, detector, processor and readout
93
x-ray sources
tubes, secondary fluorescent x-rays, radioisotopes, synchotron radiation
94
cyclotron sources
EM radiation can be generated when charged particles are accelerated radially = synchotron radiation (ie CERN)
95
short wavelength limit (eq)/duane-hunt law
Ve = hc/lambda, so lambda (in A) = 12,398/voltage
96
x-ray detector types
gas-filled transducer, scintillation counters, semiconductors, film
97
scintillation detector
NaI crystal (often) fluoresces when hit with radiation from sample. pmt counts the light
98
semiconductor x ray detector
energy dispersive, multiple layers to disturb e- and carry signal to amplifyer
99
calculating mass absorption coefficient for a compound
%element*mass abs coefficient
100
releasing agent
cations that bond to atoms that would otherwise form non-volatile complexes with the analyte, preventing analysis
101
protective agents
form volatile compounds with the analyte so it can be measured in spite of the presence of other spp
102
ionization suppressors
reduce ionization by providing a source of e- so the species will go back to elemental form
103
hollow-cathode lamp
most common AAS source. light is produced by metal atoms that have been excited by inert gas from electrical stimulation
104
sputtering
process within hollow cathode lamp where the metal produces an atomic cloud
105
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)
106
spectral interference
very close interference that cannot be resolved with the peak of the analyte
107
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.
108
solute-volatilization interference
changes in solute volatility based on presence or absence of another species.
109
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
110
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
111
arc vs spark spectra
arc is low temp (4000) and has atomic lines, spark is very high (40000) and has ionic lines
112
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.
113
energy dispersive x-ray fluorescence spectroscopy
uses multi-channel detector, measures radiation of diff spp using monochromator (DCC) before sample. worse resolution than WD.
114
wavelength dispersive x-ray fluorescence spectroscopy
has 2 DCCs (before and after sample), focuses to spec wavelength. leads to higher resolution
115
DCC
doubly curved crystal, monochromator for x-ray spec
116
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
117
hkl in problems
given as peak XXX (hkl)
118
extended x-ray absorption fine structure
tells configuration of atoms
119
x-ray absorption near edge structure
probes oxidation state (valence)
120
gas filled transducer
x-ray detection method where when gas is ionized by x-rays it conducts`
121
semiconductor x ray detectors
are electric. can use CCD (charge coupled) or lithium-drifted silicon
122
eq for lattice edge length
d = a/sqrt(h^2+k^2+l^2). a is lattice constant = cube edge length
123
natural width of atomic emission line
10^-5 nm (only due to uncertainty principle)
124
excitation for as
for flour it is wavelength, for AES it is thermal
125
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.
126
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)
127
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
128
for x ray crystal edge questions
dont forget it's VOLUME!!
