Final material Flashcards
___________ is considered electromagnetic radiation (EMR), a form of energy described with both wave and particle properties.
Light
_______consists of oscillating electric and magnetic fields (perpendicular to one another) that travel linearly through space at a constant speed. In a vacuum, the speed of light is 2.99792x108 m/s … but for simplicity, we’ll use 3.00x108 m/s
EMR
The wave properties of light are described by its ______________________. There is a constant and inverse relationship between frequency and wavelength defined by the speed of light, c.
frequency (ν), wavelength (λ), and amplitude (A e)
c = _______, where wavelength is in meters and frequency is in s-1 (the Hertz unit is 1/s). The wave number, ̅ 𝜐𝜐, is defined as 1/λ and is usually in units cm
λν
The energy of a light wave or particle (photon) is defined using Planck’s constant(h), where h = 6.626x10-34 J·s
6.626x10-34
E = hν = ?
hc/λ = hc ̅
We can use __________ as a signal source in many spectroscopic methods, either by measuring photons from a reaction or process, or by converting energy into photons and measuring them.
photons
Some methods also convert photons into ________ in order to provide an electrical signal that can be measured and interpreted by an instrument
electrons
Photons can be absorbed by _________ – either by atoms or molecules
matter
Photons can be __________ by matter – either by atoms or molecules
emitted
__________ can occur as photoluminescence (emission after absorption) or chemiluminescence (emission after a chemical reaction)
Emission
__________ can also be reflected, refracted, diffracted, scattered, or dispersed
Photons
When sufficient energy strikes a material, an atom or molecule can be promoted in energy from a ___________ to an excited state (absorption)
ground state
__________ in an excited atom or molecule can also be released as a photon as the particle relaxes back to a ground state (emission).
Energy
In order to promote an atom or molecule from a ground state to excited state, energy must be supplied in the form of _________ (photons), heat (flame, furnace, plasma), or chemical reaction
light
Light sources can be categorized as _________ or line sources. A continuum source has light output over a wide range of wavelengths, while a line source only emits discrete wavelengths
continuum
Heat sources include a __________ , an electric furnace, a plasma ‘flame’, or an electrical arc or spark source
fuel-oxygen flame
Chemical reactions can produce heat for _______________ (e.g., glow stick) while enzymatic processes and contribute to bioluminescence (e.g., firefly).
chemiluminescence
Particularly for continuum sources, we need a way to only send or receive specific wavelengths. This is done via a wavelength selection process that can use filters or, most commonly, a _____________
monochromator
A ______________ will take a narrow beam of light (after it passed through a slit aperture) and using prisms or diffraction grating along with a series of mirrors, passes a specific wavelength of light to the sample for absorption. Light emitted
from a sample can also pass through a similar device before going to a detector
monochromator
After light is generated, split, and passes through the sample, we need to detect
the remaining light that reaches a _____________. Commonly, the photons that
were not absorbed in a sample, or photons that were emitted from a sample are
collected in such a way that they are then converted to electrical signal
detection system
A _________________ accepts a photon that strikes a photoemissive
cathode ..a specially coated surface that produces electrons when struck by
photons
photomultiplier tube (PMT)
The electrons given off by the cathode then strike a successive series of __________
that produce even more electrons. With multiple dynodes in place, a single
photon can create millions of electrons that generate an electrical current that
can be measured and interpreted by the instrument
dynodes
______________ require that there is some mechanism by which light (either
electric or magnetic field) interacts with an analyte (atom, molecule)
Absorption methods
In UV/Vis, when a photon is absorbed, its energy changes the energy of the
______________ electrons
analyte’s valence
In infrared, the absorbed energy changes the ____________ energy of a bond
(molecule)
vibrational
For an absorption event to occur, the photon’s energy (hν) must equal the energy
difference (ΔE) between two of the analyte’s energy states. Energy levels are
quantized, meaning for a transition between two levels to occur, an exact amount
of energy is required … analogous to rungs on a ladder
