2 molecular spectroscopy Flashcards
what is molecular spectroscopy and what does it do
uses the interaction between electromagnetic radiation and matter to obtain info about molecules
why is spectroscopy important
helps us find info about molecules
helps us identify compounds and how much of it is present (quantitative analysis)
bond lengths
bond angles
bond strength
what does molecular energies being quantised mean
it means that they can only be certain, discrete values
what is spectroscopy, based on quantised, discrete energy levels
spec involves the transition between then quantised, discrete energy levels
what does discrete mean
individually separated and distinct
🌳🌳🌳🌳. 🌲
what transition occurs in spec
the molecule transitioning between the quantised, discrete energy levels.
explanation or IR spec absorption bands
when radiation is absorbed due to different bond vibration in the molecule
speed of light
wavelength
frequency equation
c = wavelength x v
energy of a photon
planks constant
frequency equation
E = hv
what happens when a molecule absorbs a photon of energy
if this energy corresponds to the energy gap between initial and final energy levels, it transitions to a higher molecular energy level.
what does the spacing between energy levels depend on
the type of molecular transition
- rotational is smallest distance
- vibrational is the middle distance
- electronic is the largest distance
different molecular transitions eg: rotational, vibrational, electronic
absorb energy from…
different parts of the electromagnetic spectrum
electronic transitions absorb radiation from which part of the electromagnetic spectrum
VISIBLE + UV
molecular vibrations absorb radiation from which part of the electromagnetic spectrum
INFRARED
molecular rotations absorb energy from which section of the electromagnetic spectrum
MICROWAVE
INFRARED
electron spins absorb radiation from which part of the electromagnetic spectrum
MICROWAVES
what part of the electromagnetic spectrum do nuclear spins absorb radiation from
radio waves
which bit of the electromagnetic spectrum has the shortest wavelength
gamma rays (short WL, high V + E + V-)
x rays
UV
VIS
IR
microwaves
radio waves (large WL, small V, E, V- )
what changes are x rays involved with
changes that occur in atomic nuclei
what changes are UV and VIS involved in
transitions between electronic energy levels
why do transitions between electronic energy levels need UV VIS radiation
bc the energy level gaps between electronic energy levels are the largest!!
they need more energy to transition to them
infrared radiation is equivalent to what
transitions between vibrational energy levels
aka: equivalent to transitions involved in vibration of chemical bonds
what do microwaves correspond to
energy level gap between rotational energy transitions.
aka; energy corresponding to the transitions when a molecule rotates
what do radio waves correspond to
energy of transition associated when an electron or nucleus spins in a magnetic field.
what happens to CO2 when it’s molecular vibration changes
bond lengths and angles change
it can do the splits, streamline
bonds can get shorter or longer
what happens to CO2 when it’s molecular rotation changes
rotates - teddy bear roll
bond length and angle stays the same
