Instrumental Analysis II

What is the wavelength range and quantum transition for gamma-ray emission spectroscopy?

The wavelength range is 0.005-1.4 Angstroms, and the quantum transition is nuclear

What is the wavelength range and quantum transition for X-ray absorption, emission, fluorescence, and diffraction?

The wavelength range is 0.1-100 Angstroms, and the quantum transition is Inner (core) electrons

What is the wavelength range and quantum transition for vacuum ultraviolet absorption?

The wavelength range is 10-180 nm, and the quantum transition is bonding (valence) electrons

What is the wavelength range and quantum transition for ultraviolet-visible absorption, emission, and fluorescence?

The wavelength range is 180-780 nm, and the quantum transition is bonding (valence) electrons

What is the wavelength range and quantum transition for infrared absorption and Raman scattering?

The wavelength range is 0.78-300 um, and the quantum transition is rotation/vibration of molecules

What is the wavelength range and quantum transition for microwave absorption?

The wavelength range is 0.75-375 mm, and the quantum transition is rotation of molecules

What is the wavelength range and quantum transition for electron spin resonance?

The wavelength range is 3 cm, and the quantum transition is the spin of electrons in a magnetic field

What is the wavelength range and quantum transition for nuclear magnetic resonance?

The wavelength range is 0.6-10 m, and the quantum transition is the spin of nuclei in a magnetic field

Why must the output power of light sources be stable for reasonable time periods?

Instability can lead to noise and drift

How is the output power of light sources stabilized?

Voltage regulated sources and double beam designs

What is voltage regulated sources in terms of output power stability?

A regulated power source that ensures that the radiant power does not change exponentially with the voltage of its power supply

What is double beam design in terms of output power stability?

In a double beam design, the intensities of the two beams are measured simultaneously or nearly simultaneously so that the effect of fluctuations in the source output is largely canceled

What are the two general categories of light sources?

Continuum sources and line sources

What are the different types of continuum light sources?

Ar lamp, Xe lamp, H2 or D2 lamp, Tungsten lamp, Nernst glower, Nichrome wire, and Globar

What are the different types of line light sources?

hollow cathode lamp and lasers

what wavelengths of light does the Ar lamp produce?

100-175nm

what wavelengths of light does the Xe lamp produce?

150-900nm

what wavelengths of light does the H2 or D2 lamp produce?

175-375nm

what wavelengths of light does the Tungsten lamp produce?

350-3000nm

what wavelengths of light does the Nernst glower produce?

350-19,000nm

what wavelengths of light does the Nichrome wire produce?

900-35,000nm

what wavelengths of light does the Globar produce?

1500-40,000nm

What is a continuum light source?

Emits radiation that changes in intensity smoothly as a function of wavelength

What is a line light source?

Emit a limited number of lines, or bands of radiation, each of which spans a limited range of wavelengths

What is blackbody radiation?

A "black body" is a hypothetical object that absorbs all electromagnetic radiation falling on it and reflects none. It also emits energy across all wavelengths making the spectrum of emitted radiation continuous.

Plank's Law is one of the key laws that govern blackbody radiation, what does this law state?

It states that the intensity of radiation emitted at a specific wavelength increases with increasing temperature. In other words, as you increase temperature, the amount of light increases but the wavelength shortens.

What is a Tungsten lamp and how does it work?

An incandescent lamp consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an inert gas and a small amount of a halogen, such as iodine or bromine. The combination of the halogen gas and the tungsten filament produces a halogen-cycle chemical reaction, which redeposits evaporated tungsten on the filament, increasing its life and maintaining the clarity of the envelope.

What are the advantages of the Tungsten lamp?

Long lifespan, consistent brightness, high efficiency, and broad spectral output.

What are the disadvantages of the Tungsten lamp?

They are not suitable for dusty, flammable, explosive and corrosive environments, or places with vibration. Additionally, if they are stained with hands or oil it can reduce brightness or shorten its lifespan.

What is a Nernst glower and how does it work?

Early form of lamp that used a ceramic rod (mix of ZrO2, Y2O3, Er2O3) heated to 2,000C to achieve incandescence

What are the advantages to the Nernst glower?

The ceramic did not oxidize so it could be used outside vacuum or noble-gas environment. In addition, it produces a spectrum more like daylight

What are the disadvantages of the Nernst glower?

Not electrically conductive so required external heat source, less efficient than the Tungsten lamp

What is a globar and how does it work?

Similar to the Nernst glower but uses SiC ceramic that is heated to 1,500C.

What are the advantages of a globar?

It is used as a thermal light source for infrared spectroscopy because its spectral behavior is similar to that of a black body emitter

What is a D2 lamp?

A low-pressure gas discharge lamp that utilizes deuterium gas to emit UV light. This type of light source is commonly used when a continuous spectrum in the UV region is needed.

What is a hollow cathode lamp and how does it work?

A type of line light source with a high potential difference between an anode and a cathode that creates a plasma by ionizing a buffer gas. The ions in the plasma sputter atoms from the cathode and both the buffer gas and the sputtered cathode atoms are excited to higher energy states by collisions with other atoms in the plasma. Emission of radiation occurs as the excited atoms fall back to lower energy states. The radiation is specific to the cathode material.

What are the four critical aspects of laser action?

Pumping, spontaneous emission, stimulated emission, absorption?

What is pumping in the context of a laser?

The production of a metastable excited state due to excitation of a molecule from pumping energy (electrical, radiant, or chemical energy) and then partial relaxation

What is spontaneous emission in the context of a laser?

Fluorescence radiation from one excited molecule differs in direction and phase from the that produced by the second excited molecule. The radiation is monochromatic and incoherent

What is stimulated emission in the context of a laser?

A photon with the same energy as those produced by the spontaneous emission collide excited molecules and cause photon emission. These emitted photons have the same energy, direction, and phase of those involved in the collision with excited molecules. The radiation is monochromatic and coherent.

What is absorption in the context of a laser?

Incident light is weakened as electrons are promoted to an excited state.

Is light amplified or attenuated if the population of ground state is greater than the population of the metastable excited state?

Light is attenuated (due to absorption)

Is light amplified or attenuated if the population of ground state is less than the population of the metastable excited state?

Light is amplified (due to emission)

What is population inversion?

Population inversion is when there is a change in the normal distribution of energy states. For example, in order to achieve light amplification in a laser, pumping will create a higher population of excited states

What is refraction?

the phenomenon of light being deflected in passing through the interface of between one medium and another or through a medium of varying density. This results in the changing of direction of propagation as a result of traveling at a different speed at different points along the wave front

What is diffraction?

The process by which a beam of light or other system of waves is spread out as a result of a narrow opening or across and edge, typically accompanied by interference in the wave forms produced

Why does a prism cause dispersion of light?

The refractive index of the glass varies depending on the wavelength of the incident light. Since the light entering is made up of many different wavelengths, the different wavelengths of light leave the prism at different angles

What does the dispersion of diffracted light in a prism depend on?

Depends on the spacing of the gratings and wavelength of the light

What is a Czerny-Turner monochromator?

Device that separates different wavelengths of light from a light source. It consists of entrance and exit slits, mirrors, light disperser, and a detraction grating. Wavelength selection is achieved by rotating the grating.

What is interferometry and how does it work in the context of absorption spectroscopy?

It is the method of choice for IR spectroscopy. One mirror is moved periodically, an interferogram is created by measuring the signal at multiple discrete mirror positions. The Fast Fourier Transform (FFT) converts the time-domain signal to a frequency domain signal (aka, makes it readable)

What are the advantages of interferometry?

Unlike approaches used with monochromators (one wavelengths at a time), the interferometer measures many wavelengths simultaneously. In addition, it is capable of providing very high resolution. Signal averaging also allows for improvements in the signal to noise ratio.

In Fourier transform spectroscopy, what is the curve decomposed into?

It is decomposed into a sum of sin and cos terms (called a Fourier series)

What is atomic spectroscopy?

The study of electromagnetic radiation absorbed and emitted by atoms. It is used to determine elemental composition

What is a photomultiplier tube and how does it work?

It is a type of detector for ultraviolet radiation and visible radiation. It works using incident photons to strike a photocathode material and generate electrons via the photoelectric effect. Electrons are then directed by a focusing electrode toward the electron multiplier where an electron cascading effect is achieved by secondary emission. This amplifier the original signal until it produces a measurable current at the anode

What is the same and what is different in energy level diagrams of different elements?

The types of transitions are similar, but the energies of the transitions are not the same

What are quantum mechanical selection rules in the context of an energy level diagram?

They predict what transitions are likely to occur as transitions can only occur between certain energy states. Transitions with low probability are considered "forbidden"

Pertaining to emission of radiation in general, what is a line spectra?

Sharp well-defined peaks caused by emission from individual excited atoms that are well separated in the gas phase

Pertaining to emission of radiation in general, what is a band spectra?

Bands that arise from numerous (quantized) vibrational levels superimposed on the ground state electronic energy level of a molecule. Radiation from electrical or thermal excitation of polyatomic species nearly always is the result of a transition from the lowest vibrational level of an excited state to any of the several vibrational levels of the ground state. This is more common for molecular species.

Pertaining to emission of radiation in general, what is a continuum spectra?

Continuous thermal (blackbody) radiation created when solids are heated to incandescence (aka, a rainbow)

What are the three factors that can influence linewidths in an emission spectrum?

Line broadening due to the uncertainty effect, doppler broadening, and pressure broadening

What is line broadening due to the uncertainty effect?

Broadening of a line due to the uncertainty principle and the relationship between uncertainty in frequency and in the lifetimes of lower and higher energy states

What is doppler broadening?

At high temperatures, atoms and ions are moving at a higher velocity. The wavelength of radiation emitted or absorbed decreases if motion of an atom is towards the transducer and it increases if the motion is away from the transducer

What is pressure broadening?

At high pressures, collisions between excited atoms and ions cause slight shifts in emission lines

Would a larger number of species in the excited state be more useful or absorption or emissions spectroscopy?

Emission spectroscopy

Would a larger number of species in the ground state be more useful or absorption or emissions spectroscopy?

Absorption spectroscopy

What are the three types of atomization in atomic spectroscopy?

Flames, furnaces, and glow discharge

What are flames in the context of atomization in atomic spectroscopy?

Usually air-acetylene(2300C) or nitrous oxide- acetylene(2700C). A sample solution is nebulized to create an aerosol, mixed with flame gas-mixture, the solvent is then evaporated, and the sample is atomized in the flame

What are furnaces(electrothermal vaporization) in the context of atomization in atomic spectroscopy?

Samples are introduced to small graphite or pyrolytic carbon coated graphite tube which can then be heated to vaporize and atomize the analyte

What is glow discharge in the context of atomization in atomic spectroscopy?

Plasma is formed by the passage of electrical current through a low-pressure gas. Positive ions strike a cathode with sufficient force to eject particles of the material on the cathode

What is inductively coupled plasma?

A plasma that is generated and sustained by electric currents which are produced by a magnetic field from an induction coil. Can reach temperatures of 6,000K

What are microwave plasmas?

A plasma that is generated and sustained using the magnetic field produced by a microwave source. Can reach temperatures od 3,000K

What is plasma in the context of spectroscopy?

An electrically conducting gaseous mixture containing a significant concentration of cations and electrons

What is laser ablation?

Ablated material is converted to plasma

What is laser induced breakdown spectroscopy?

Laser power is sufficiently high to cause dielectric breakdown of the atmosphere around the ablated material and creates a localized luminous plasma