Test 2 Flashcards
sig figs for 5
(any integer) 0
T eq
P/Po
A eq (not beers law)
A = -logT OR log(P0/P)
rule for log sig figs
log(x) = 1.x
P
Watts/cm^2
molar absorptivity units
1/cm*M
chemical deviations from beers law
epsilon changes for indicator reactions, intermolecular complexes created due to high conc
pKa
can give you Ka for ratio
instrumental deviation from beers law
stray light or polychromatic light
stray light eq and info
more stray decreases signal (A), A= log ((Po + Ps)/(P + Ps))
polychromatic light deviation
can be up or down from linear, add the initial powers of light over the other powers of both for T
light sources
H/D lamps visible light, Xenon peaks at 500 nm, W goes up to 2500 nm
Noise sources for spectrometer
source, absorption, intensity loss from wavelength selection, photoelectric transducer noise (all propagate)
silicon photodiode
silicon chip with a depleted layer (pn junction) that radiation can enter and go to the electrodes. used for low radiation, portable. more sensitive than a phototube but less than a photomultiplier tube
CCD vs multichannel photon detectors
CCD is 2d (grid is scanned) while multichannel is 1D (rows in a line)
double beam reduces..
fluctuation, deviation from source wavelength (simultaneous)
photodiode array
double beam, fast response (good for kinetics). multiple photodiodes form an array and circuit. they act as pixels, 1000ish together does the whole spectrum very quickly (simultaneously)
I and Io
dependent for double beam, independent for single beam
dependent values prop of error for A
A = log Io - log I
error in single and double beam
error compounds for single beam, it cancels to 0 for double
error canceling equation
sigmaA^2 = sigma(logIo)^2 + sigma(logI)^2 - 2sigma(ab) using the errors
error through spectrometry equation
Sf = Ilamp* L* Sample * Spt
calculating molar absorptivity
8.7x10^19(P)(A) where P is transitional probability (0-1), A is target cross sectional area for photon of whatever wavelength to interact with, around 10^-15 cm^2 for organic molecules
quantum jump
e- changing energy levels. prob determined by transitional prob, below 0.01 not happening, 0.1to 1ok
solvent effects
can make peaks more diffuse due to strong solvent interactions
why is absorption good for quantitative analysis
widely applicable, sensitive (10^-4-10^-7 M), fairly selective, 1-3% uncertainty, easy to do.
method for spectrometry
find lamba max, look at variables: solvent, pH, temp, electrolytes, interfering species, then clean cell before using
standard addition use
reduces matrix effects
standard addition procedure
usually 5 replicates, know volume and the amount of standard added to learn the initial concentration
beers law graph SHOULD
pass through 0
sig figs for error
should match the # for the value
deuterium vs hydrogen lamps
continuum, UV. deuterium creates a more intense light
filter vs monochromator
filters are cheaper and retain intensity, but are specific to a wavelength. monochromators can be adjusted but leads to a drop in intensity and more costly
photovoltaic cells
visible light range, common. copper or iron with semiconductor layer, and gold or silver outside that which e- liberated at semiconductor Flow through so current tells us # of e-. cheap, but low resistance and fatigue (current dec during continued use)
phototubes
resistance is high so they can amplify. voltage of e- goes through wires to anode, when saturated the amount of current corresponds to light intensity. made for many ranges of light nm
photomultiplier tube
light hits a small area and disturbs e- which disturb surrounding e- in the material, amplifying the signal.con: cannot take intense light
time vs space double beam
time needs 1 detector, space needs 2
photometers vs spectrophotometers
photometers use filters, spectro use monochromators
multichannel spectrophotometers
very fast, use electronic rather than manual scanning
titration stages
in A + T gives P, at start all A, then A + P, then all P at endpoint and past endpoint T + P
inconsistencies with Einsteins calculations
atoms do not necessarily start with all atoms at ground state
eigenstate
value for an e- at which it can exist, only has specific quantities (stable)
scattering
energy goes in and instantly leaves
stimulated emission
light enters and emission occurs
virtue states
unstable values at which an e- can exist (leads to scattering)
phosphorescence is when..
singlet state moves to triplet.
singlet state
all e- paired, no split orbitals on magnetic contact (diamagnetic)
diamagnetic
0 net magnetic field, e- are stably repelled by their respective fields
paramagnetic
moment of attraction w magnetic field due to unpaired e-
spin multiplicity =
2S +1 (for e- of same spin)
triplet state
e- unpaired, spin multiplicity, more stable than singlet even when excited
delta S =
0 (magnetic QNs should add to 0)
lines on Jablonski diagram are..
Eigenstates
internal conversion
molecule dec energy state by intramolecular processes
singlet vs triplet radiation
singlet is very short(<10-5 s) triplet is longer (10-5 to full seconds)
fluorescence vs phosphorescence
f has high quantum yield, can work in most temperatures and 0 e- spin and singlet-singlet transition shorter than 10-5 sec, p has low quantum yield at low temp and +/-1 e- spin, singlet state moves to triplet (longer than 10-5 sec).
stokes shift measurement
distance between the max values for absorbance and emission
quantum yield
luminescent molecules/# total excited molecules
quantum yield approaches 0 as..
radiationless decay rate is much smaller than radioactive decay
power of fluorescence eq
F =K’ (Io-I), K is related to QY, transforms to If = K’Io(1-10^-Ebc), if Ebc < 0.05, linear version If = logK’IoEbvc…. therefore Io inc fluorescence.
T vs A
T is multiplied as more parts are added, A is additive
external conversion
molecule dec energy state by intermolecular processes
intersystem crossing
energy level change causes a change in electron spin, which changes multiplicity (usually triplet to singlet) but has a very similar energy
excitation graph spectrum
one wavelength of emission shows peak at a wavelength of input(x axis is diff input wavelengths)
rigidity and fluorescence
more rigid = higher quantum yield, more fluorescence
power of fluorescence covaries with
K (includes quantum yield, emission lambda, initial intensity (from excitation lambda), b, a constant), and conc.
for better linear shape, this level of conc is best
LOWER (for luminescence)
excitation spectrum uses
constant emission wavelength (they only look at one wavelength and how emission there changes as the excitation beam takes on different wavelengths)
emission spectrum uses
constant excitation wavelength
phosphorescence vs fluor energy
for the same (natural) molecule, lower energy and quantum yield
fluorophotometer equipment setup
excitation monochromator, emission monochromator, can be sequential or double. can also be filters
phosphorescence detector setup
excite radiation, chopper blocks light from hitting sample while it fluoresces, then detector gets phosphorescence
measured variable in fluorometry
always emission
sensors and fluorescence
have smth that binds to species of interest and then fluoresces
chemiluminescence
luminescence from product of a reaction (emits when produced due to energy, no excitation is needed)
fluorescence applications
detects GFP! can have fluorescent binding to DNA etc to detect it
laser
light amplification by stimulated emission of radiation
energy conservation for laser
must put in energy to get energy
spontaneous emission examples
fluorescence and phosphorescence. they emit right after they have input
stimulated emission
used in lasers, e- must be excited and get an additional input to give off twice the excitation beam w energy conserved
metastable excited state
this is needed for a laser. population inversion allows the excited state to have a constant population (it is changing but there are always a similar number)
parts for laser
power supply, pumping source, mirrors on both ends, lasing medium in middle
pumping
excitation of the lasing medium (can be electric, heat, chemical)
how does laser create coherent radiation
photon hits excited e- on lasing medium > 2 photons in phase with one another are produced
absorption in laser
when non excited molecules pick up a photon and become excited, this competes with stimulated emission (takes photons from the source/previous emissions)
wavelength amplified by laser is determined by
the cavity size
population inversion
majority of molecules are excited (not ground state) and thus can emit coherent photons. required to sustain laser beam
4 level laser
has 2 intermediate energy levels, one at which no e- can stay and a higher one that must be reached for pop. inversion, but the number only needs to be higher than the number in that transient state (0). so it is easier to sustain inversion, more widely used
3 level laser
for pop inversion you need to have more in the intermediate than ground state and so many molecules are ground state that it is harder to achieve this
first laser
solid state, ruby
gas laser types
neutral atom, ion, molecular (gases like N2), eximer
eximer laser
ion complex of a normal ion and a noble gas that is only stable when excited, this makes inversion very easy (any amount of pumping)
solid vs gas lasers
solid lasers can be much more compact
IR setup
same as absorbance, just reports in wavenumber
IR given off by (in graphical form)..
the vibrational relaxation in Jablonski diagram
how to tell if IR active
FIRST draw molecular shape. dipole must change (not net 0)
selection rule - vibration
IR absorption occurs when there is vibration bc the emission matches the vibration and it is able to absorb (changes amplitude) so it wont absorb without a dipole change (IR active vibration)
dipole moment eq
mu = qR, mu = dipole moment, q = charge, R = distance, so if distance changes non symmetrically it will change.
frequency with force constant
f= 1/2pi sqrt(k/mu)
wave number eq
v = 1/2pi(c) sqrt(k/mu)
k (force/strength) and carbon-carbon bonds
high for single, drops for double, climbs a bit for triple
v
the vibrational qn, can be 0 or more
fundamental transition
moving 1 energy level (deltaV=1)
anharmonic oscillators
transition plus of minus 2 or 3 = create overtones
transition selection rule
only 1 peak for a molecular vibration due to energy level spacing (normal modes of harmonic are +/-1)
normal modes for polyatomic molecule
3N-6
normal modes for linear
3N -5
vibrational coupling
an atom btwn two stretching bonds or bond btwn two atoms involved in bending or connecting 2 different motions couples the vibrations. must be close together and fairly close in energy - one peak (i think)
IR radiation sources
inert solid heated up
IR detectors
thermal, pyroelectric, photoconducting
new tech in IR
lamp is also the wavelength selector
fourier transform spectrometer
source > sample > selector > detector but all surrounded with mirrors, one moves and changes the lambda when needed. not dispersive, a lot of light reaches the detector. high resolution (you can see every tiny peak), and most importantly can read whole spectrum VERY FAST so potential S/N can be tiny. also records in time domain so graph is the wave of the radiation
michelson interferometer
transducer in fourier spectroscopy, time domain to space domain, measures interference in time domain and modulates signal to be read in space bc it is usually too high freq and space is lower.
quantum vibration eq (Energy)
E = (v+ (1/2)) (h/2(pi))sqrt(k/mu) where v is the qn.
thermal IR detector
heats up, susceptible to thermal noise
pyroelectric IR detector
dielectric materials have thermal and electrical effects. change in conductivity when radiation hits them. very fast
photoconductor IR detector
absorbs radiation in non-conducting e- which become conducting, decreasing resistance in unit when radiation is detected
dispersive IR spectrophotometers
usually have a chopper to discriminate noise, but same design as spectrophotometers
mirror drive resolution eq for FTIR
delta v (diff btwn wavenumbers) = 1/delta , where delta is the retardation = 2x distance of mirror drive
predissociation
an internal conversion releases vibrational energy large enough to break a bond, more likely in larger molecules
dissociation
absorbed radiation excites an e- to a high enough energy level that a bond is broken
why is fluorescence better that absorbance in detection
only intensity of source light can be inc and the measurement of intensity will inc for fluoro. for spectrophotometry since there is P and Po the ratio cannot be changed as much (= just light from a source vs being forced to measure transmission
pi vs other transitions
n = non-bonding, pi = pi orbitals, sigma = sigma orbitals. so sigma sigma* is excitation of a single bond (out of UVVIS range), n to pi* is less energetic than pi to pi* (shorter distance), so the double bond is favored for more fluorescence compared to non bonding e- in same process.
FTIR spectrometry is better for…
resolution, high absorption spp, weak absorption spp, kinetics (it is very fast), very small samples, IR emitting samples
how to do refractive index
it is a percent transmittance basically, so multiplicative. %lost = og(n1-n2/n1+n2)^2
retardation in FTIR
retardation (delta) = 2(movable mirror-fixed)
mirror drive distance FTIR
1/delta = wavenumber, distance = delta/2
inferogram time frequency for michelson interferometer
2(vm)/lambda aka 2(vm)v/c where vm is velocity of mirror
tau in michelson interferometry
time for a wave, 1/f
what is the fourier transformation
spatial information converting to frequency
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
wagging
ligand moves out of the plane towards viewer
scissoring
in non linear, central moves down and sides move up/out (2 bending vibrations)/ligands bend in opposite directions
vm and tau
vm*tau = lamba/2
twisting
one ligand moves into the plane the other out
rocking
ligands bend (2 bonds attached to 1 A) in same direction
laser eq
lambda = 2L/n where L is cavity length
std dev for measurements eq
the RSD based on S/N (= 1/S/N) times 0.434 = std deviation
reduced mass (mu)
m1*m2/(m1+m2) < all in kg.
