Spectrometric Methods Flashcards

Flashcards covering key concepts from the Spectrometric Methods lecture.

What are the general properties of electromagnetic radiation?

Electromagnetic radiation can be depicted as an electromagnetic wave showing electric and magnetic vectors, amplitude, and wavelength, but this does not explain particle effects of light such as photons and the photoelectric effect.

In spectrophotometry, which vector is most important?

The electric vector (absorption).

Which wave is responsible for the absorption of RF waves in NMR?

The magnetic wave.

What are the interactions of light with matter?

Absorption, Reflection, Refraction, Diffraction, and Scattering.

What type of light scattering involves scattered light having the same energy (wavelength)?

Elastic scattering, also known as Rayleigh Scattering.

What is diffraction of light a consequence of?

Interference of light waves.

What happens to wavelength as light goes through matter?

As light goes through matter, if the velocity (c) and frequency (n) are fixed, then the wavelength (l) will change.

What units are used in the UV-Vis region of the spectrum, and what unit is used as it gets longer (IR)?

In the UV-Vis region, nanometers (nm) are used. As the wavelength gets longer, wavenumbers (cm-1) are typically used.

What is the equation for a wave?

y = A sin(wt + f), where y = magnitude of electric field, A = amplitude, f = phase angle, and w = angular velocity.

What occurs when two light waves are superimposed?

Constructive and destructive interference.

What happens to waves when they go through a slit?

With a wide slit, the waves go through mostly unchanged. With a decreased slit, there is more diffraction, making it seem as if the source of the wave is a new source.

What is required for coherent radiation?

Identical frequencies and a constant phase relationship between the beams.

What is the general expression for light bands surrounding a central band in diffraction?

nl = BC sin q, where n = order of interference, q = angle of diffraction, and BC = distance between the slits.

What is used in modern spectrophotometers to separate wavelengths of light?

A diffraction grating.

What happens when light passes through anything but a vacuum?

The frequency of the light is changed, but not the energy. This is given by the refractive index of the material.

Define polarization in the context of light transmission.

Polarization refers to the temporary deformation of the electron clouds of the atoms in the medium.

What effect occurs when you have a change in the refractive index?

You get a reflection and losses of the intensity of the light.

What is the photoelectric effect?

The method by which photons of light are converted to an electrical signal.

What device uses the photoelectric effect to detect light?

The photomultiplier tube.

What is the function of a photomultiplier tube?

A photoemissive device in which the absorption of a photon results in the emission of an electron, amplifying weak light signals.

What is the function of the photocathode in a photomultiplier tube?

Releases electrons when exposed to a photon flux.

What is the function of dynodes in a photomultiplier tube?

Electrodes that multiply the number of electrons emitted by the photocathode.

What is the equation for the kinetic energy of the lowest emitted electron?

KE = hn - w, where w = work function.

What happens to a metal if more KE than the work function is imparted?

The metal will emit an electron in response to the photon.

What happens during emission or chemoluminescence?

The sample's electrons are excited to a higher orbital and generate a photon as the electron de-excites.

What happens during elastic scattering?

Incident radiation hits a particle and scatters in all directions at the same wavelength.

What happens during inelastic scattering?

The scattered light loses or gains energy and scatters the light at different wavelengths. This is known as Raman Scattering.

What is a continuous spectrum?

A range of light from the blue to the red, such as sunlight or light from glowing filaments.

How do atoms, ions, or molecules absorb radiation?

Electromagnetic radiation is transferred to the particles, promoting them from a ground state to a higher energy excited state. They can only absorb specific discrete energies.

What is the simplest spectrophotometer?

A filter photometer. The filter blocks out all but a small band of light so that some quantitation can be done.