electronic spectroscopy + IR Flashcards
photoelectron spectroscopy has enough energy to do what
enough energy to ionise
what is einsteins equation involving hv
planks x frequency =
ionisation energy x kinetic energy
what does hv = Ke + Ie tell us
that if we know a photons energy and it’s kinetic energy, we can find it’s ionisation energy
what is the process of photoelectron spectroscopy
shining hv on a sample ionised it and causes it to lose an electron
what is hv
energy of a photon
what does XPS stand for
x-ray photoelectron spectroscopy
what is x-ray photoelectron spectroscopy used for + characteristics
- identifying chemical elements present and their environments
- quantitative
- surface selective
ratio of surface to bulk
1 : 10^8
electronic spectrum of the H atom emission spec diagram exp
promoted electron falls to lower energy level and emits a photon.
light is seen as this occurs.
what is an alpha transition
lowest energy transition
the energy level right above the ground state
what is the alpha transition for the lyman series
2
what is the alpha transition for the ballet series
3
what is the alpha transition of the paschen series
4
what is the series limit transition
energy when electron falls from infinity to ground state
highest energy transition
what light is lyman
UV
level 1
what light is balmer
visible light
level 2
what light is paschen
infrared light
level 3
what does the series limit correspond to
the ionisation energy
from the alpha transmission to the series limit transition, what happens to the energy spaces between then
they get smaller
the energy difference is smaller
when light emitted is plotted against energy where does each series go
paschen = smallest energy, all lines have the same light intensity
balmer = middle, all lines have the same light intensity
lymann = highest energy, the same light intensity
in hydrogen atom emission spectra, what series had the highest wavelength
lymann = shortest
balmer = middle
paschen = longest
what is the rydberg equation for v- aka wavenumber
Rh = (1/smaller n2 - 1/larger n2 )
rydberg constant value and units
1.097 x 10^5 cm-1
what is the n1 aka smallest n value for the different series when finding v- wavenumber using the rhydberg equation
lymann = 1
balmer = 2
paschen = 3
these are the lowest energy levels the electron can fall to.
what is n2 aka the largest number that an electron can fall from for each series
infinity
worded rhydberg equation
wavenumber = rhydberg constant x (1/ where e- is falling to squared) - (1/ where electron is falling from squared)
in cm-1
infinity 2 gives what value
0
what happens in UV VIS spec
absorbance of light or radiation excited electrons from group state to the first excited stage of the compound.
go to the anti binding orbital??
isobestic point
no intermediates
molecule / state changes to another directly
seen in UVVIS spec
IR radiation can do what to molecules
cause a shape change
stretch and bend them.
when an atom is pulled apart to its max it has what
maximum extension
LARGE POTENTIAL ENERGY
when an atom is at its normal bond length is has
minimum extension
minimum potential energy??
r is theeee
the bond length
what is the harmonic oscillator
U shape
shows relationship between potential energy and r (bond length)
harmonic oscillator explanation
as bond distance increases, potential energy decreases to a trough then increases again
we can only oscillate smt atttt
particular energies
what is oscillation
back and fourth rhythmic movements
vibrational energy is
quantised
equation to show how vibrational energy is quantised at energy level V
Ev = hw ( v + 1/2)
where v is a quantum number for vibrational level (1,2,3,4)
h is planks constant
w is fundamental frequency (s-1)
energy for vibrational level 1
E1 = h w (1 + 1/2 )
= 1.5 hw
what is hw
fundamental frequency
when energy is plotted against distance u get a parabola for potential energy. the distance between vibrational levels is
hw
zero point energy
V=0
E0 = hw (0 + 1/2)
= 1/2 hw
this is bc a molecule cannot have 0 vibrational energy
change in energy between 2 diff vibrational energy levels
Change in E = final - initial values
values = answers to Ev = hw (V + 1/2 )
what is w and it’s units
fundamental frequency
s-1
how can we find the fundamental frequency, w
W = 1/2🥧 x 🟫🌳 k/ reduced mass
k is the
force constant
aka strength or the spring
if there’s a larger k value that means there is a larger
w value
what is reduced mass for a bond between 2 diff molecules // 2 of the same molecules in kg
(M1)(M2) / M1 + M2
when finding the M1 and M2 what must we do
mass of atom / avogadros constant
then apply it to M1 and M2
selection rule for IR SPEC
gross selection rule
what is the gross selection rule
in order to interact with infrared radiation, a vibration must have a changing dipole
how many independent directions can an atom move in
3
along the x, y, z axis
total degrees of freedom = 3N
where n is the number of atoms.
what is the other specific selection rule
in a simple harmonic oscillator, the change in V can only be -+1
u cannot jump 2 levels
