CHEM 3111 | Spectroscopy

wavelength symbol

λ

frequency symbol

v

energy equations

E = hc/λ (for one photon; 6.022 × 10²3 photons = 1 mol)

E = hv

in molecular absorption, energy ___ and is ____

increases, excited

in molecular emission, energy ____ and is _____

decreases, relaxed

visible region of light

400-700 nm

the highest energy molecular process that occurs when a molecular absorbs a microwave photon is ___

rotation

the highest energy molecular process that occurs when a molecular absorbs a infrared photon is ___

vibration

the highest energy molecular process that occurs when a molecular absorbs an ultraviolet photon is ___

electronic excitation

the highest energy molecular process that occurs when a molecular absorbs an x-ray photon is ___

bond breaking

cancer :(

singlet state

no spin flip (faster)

triplet state

spin flip occurs (slower)

the first thing a molecule does when it absorbs is ____

relaxes

energy hierarchy

electronic excitation, vibration, rotation

any time a photon gains energy/becomes excited, it also changes the rotation and vibrational energy as a result

radiative process

photons are involved

nonradiative processes

no light emitted; energy lost as heat

rigid, sp2 hybridized molecules can’t relax as easily and need to ____ or _____

fluoresce or phosphoresce

does fluorescence involve spin flip?

no (shorter duration)

Stokes shift principle

Emission (energy released) always occurs at a LONGER wavelength than absorbance

Absorbance involves energy increase; shorter wavelength

Absorbance and transmittance have an inverse _____ relationship, where absorbance measures the light _____ by a sample and transmittance measures the light that ____ through

log, absorbed, passes

measuring luminescence differs from measuring regular light because it picks up ____ photons only, not transmitted photons

emitted

90 degrees

an ideal blackbody is an object that

absorbs all the energy that strikes it and emits light based off temperature (sun)

continuum sources

emits light at a large range of wavelengths

line sources

emits light only at specific wavelengths (laser)

monochromator

instrument that isolates white light into the visible spectrum and selectively isolates one wavelength (based on angle)

reflective or transmissive optical device w closely spaced lines

resolution

the ability of a spec to distinguish between two closely spaced wavelengths

minimum wavelength difference between 2 peaks that can be distinguished

resolving power (N) formula

λ/Δλ = nN

λ = avg of two wavelengths

Δλ = resolution (difference between two wavelenths)

n = defraction order

N = number of grooves (resolving power)

phototubes

phototubes produce electric currents when hit by transmitted light (light → electricity)

weak current

photomultiplier tubes

amplifies current in phototubes

electrons are accelerated when they hit a dynode (mario kart)