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Forensic Science Word Study
Chapter 5 – Spectroscopic Techniques
Directions: Study the following words by reading and rereading them each evening so you will be
prepared for the word study test each week. You may use one index card to write as many words
and definitions on as possible to use for the test. The card must written in ink, be in your
handwriting, and have your name, your class period, and the chapter recorded in the top, right
corner with no obvious erasures or mark outs. ALL WORDS MUST BE NUMBERED. If all the
criteria are met, you may use your index card during the test. It will then be stapled to your test.
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Atomic absorption spectroscopy (AA) – in analytical chemistry is a technique for
determining the concentration of a particular metal element within a sample.
Atomic absorption spectroscopy can be used to analyze the concentration of
over 62 different metals in a solution.
Absorption spectrum – a continuous spectrum that passes through a cool gas has
specific spectral lines removed (inverse of an emission spectrum)
Atomic spectroscopy – the determination of elemental composition by its
electromagnetic or mass spectrum. The study of the electromagnetic spectrum of
elements is called Optical Atomic Spectroscopy. Electrons exist in energy levels within
an atom.
Attenuated total reflectance (ATR) – a sampling technique used in conjunction with
infrared spectroscopy which enables samples to be examined directly in the solid or liquid
state without further preparation.
Chemical shifts – In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift
is the resonant frequency of a nucleus relative to a standard. Often the position and
number of chemical shifts are diagnostic of the structure of a molecule.
Conjugated bond – is a system of connected p-orbitals with delocalized electrons in
compounds with alternating single and multiple bonds, which in general may lower the
overall energy of the molecule and increase stability.
Conjugated carbon/carbon double bond – a system of connected p-orbitals with
delocalized electrons in compounds with alternating single and multiple bonds, which in
general may lower the overall energy of the molecule and increase stability. Lone pairs,
radicals or carbenium ions may be part of the system. The compound may be cyclic,
acyclic, linear or mixed.
Covalent bond – a chemical bond that involves the sharing of electron pairs between
atoms. The stable balance of attractive and repulsive forces between atoms when they
share electrons is known as covalent bonding.
Cuvette – a straight-sided, optically clear container for holding liquid samples in a
spectrophotometer or other instrument.
Diamond cell – a device used in scientific experiments. It allows compressing a small
(sub-millimeter sized) piece of material to extreme pressures.
Diffuse reflectance – the reflection of light from a surface such that an incident ray is
reflected at many angles rather than at just one angle as in the case of specular reflection.
Elastic - the energy of the scattered photo is the same as that of the incident or absorbed
photon in the Raman effect.
Inelastic – the energy of the scattered photon can be greater or less than that of the
incident one.
Electromagnetic radiation – a kind of radiation including visible light, radio waves,
gamma rays, and X-rays, in which electric and magnetic fields vary simultaneously.
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Electromagnetic spectrum – the entire range of wavelengths or frequencies of
electromagnetic radiation extending from gamma rays to the longest radio waves and
including visible light
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Electron – a stable subatomic particle with a charge of negative electricity, found in all
atoms and acting as the primary carrier of electricity in solids.
Emission – the process by which a higher energy quantum mechanical state of a particle
becomes converted to a lower one through the emission of a photon, resulting in the
production of light. The frequency of light emitted is a function of the energy of the
transition.
Energy (E) – is the capacity of a physical system to perform work. Energy exists in several
forms such as heat, kinetic or mechanical energy, light, potential energy, electrical, or
other forms. According to the law of conservation of energy, the total energy of a system
remains constant, though energy may transform into another form. Two billiard balls
colliding, for example, may come to rest, with the resulting energy becoming sound and
perhaps a bit of heat at the point of collision.
Emission spectroscopy (ES) – refers to the range of wavelengths emitted by
an atom stimulated by either heat or electric current.
Excitation – in physics, the addition of a discrete amount of energy (called excitation
energy) to a system—such as an atomic nucleus, an atom, or a molecule—that results in its
alteration, ordinarily from the condition of lowest energy (ground state) to one of higher
energy (excited state).
Frequency (v) – refers to how often the particles of the medium vibrate when a wave
passes through the medium.
Gamma ray – Gamma radiation, also known as gamma rays, and denoted by the
Greek letter γ, refers to electromagnetic radiation of extremely high frequency and
therefore high energy per photon. Gamma rays are ionizing radiation, and are thus
biologically hazardous. They are classically produced by the decay from high energy states
of atomic nuclei (gamma decay), but are also created by other processes.
Hertz – (Hz) is a unit of frequency, defined as the number of complete cycles of a periodic
signal that take place in one second. For example, the frequency of sound waves is usually
reported in units of Hertz.
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Inductively coupled plasma mass spectrometery (ICPMS) – a type of mass
spectrometry which is capable of detecting metals and several non-metals at
concentrations as low as one part in 1012 (part per trillion).
Infrared – the part of the electromagnetic spectrum having a wavelength just greater
than that of the red end of the visible light spectrum but less than that of microwaves.
Infrared radiation has a wavelength from about 800 nm to 1 mm, and is emitted
particularly by heated objects.
Infrared (IR) spectroscopy – the analysis of infrared light interacting with a molecule.
This can be analyzed in three ways by measuring absorption, emission and reflection. The
main use of this technique is in organic and inorganic chemistry. It is used by chemists to
determine functional groups in molecules. IR Spectroscopy measures the vibrations of
atoms, and based on this it is possible to determine the functional groups.5 generally,
stronger bonds and light atoms will vibrate at a high stretching frequency (wavenumber).
Infrared microspectophotometry – a technique, routinely used in various applied
fields, with an optical system consisting of IR spectrometer and microscope optical module.
A color charge-coupled device camera is able to capture the optical image of the inclusions
under investigation.
Ionic bond – the complete transfer of valence electron(s) between atoms. It is a type of
chemical bond that generates two oppositely charged ions. In ionic bonds, the metal
loses electrons to become a positively charged cation, whereas the non-metal accepts
those electrons to become a negatively charged anion.
Mass spectrometry – A process used to identify chemicals in a substance by
their mass and charge. Mass spectrometers are instruments that measure mass and charge
of molecules. A mass spectrometer also can determine how much of a compound is
present in a mixture.
Matrix assisted laser desorption ionization (MALDI) – a recent desorption/ionization
technique used in mass spectrometry. Analyte molecules are dissolved into a solution of
solvent and UV-absorber. A drop of this solution is allowed to dry to form a solid crystalline
matrix on a metallic pin and then inserted into the vacuum system.
Microwave – an electromagnetic wave with a wavelength in the range 0.001–0.3 m,
shorter than that of a normal radio wave but longer than those of infrared radiation.
Microwaves are used in radar, in communications, and for heating in microwave ovens and
in various industrial processes.
Molecular fluorescence – the optical emission from molecules that have been excited to
higher energy levels by absorption of electromagnetic radiation.
Monochromator – an optical device that transmits a mechanically selectable narrow band
of wavelengths of light or other radiation chosen from a wider range of wavelengths
available at the input.
Nernst glower – an obsolete device for providing a continuous source of (near) infrared
radiation for use in spectroscopy.
Neutron – a subatomic particle of about the same mass as a proton but without an electric
charge, present in all atomic nuclei except those of ordinary hydrogen.
Nucleus – the positively charged central core of an atom, consisting of protons and
neutrons and containing nearly all its mass.
Orbital – each of the actual or potential patterns of electron density that may be formed in
an atom or molecule by one or more electrons, and that can be represented as a wave
function.
Photocell – SOLID-STATE DEVICE with a photosensitive CATHODE that emits
ELECTRONS when illuminated and an ANODE for collecting the emitted electrons.
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Illumination excites electrons, which are attracted to the anode, producing current
proportional to the intensity of the illumination. In a photovoltaic cell, light is used
to produce voltage.
Photon – a particle representing a quantum of light or other electromagnetic radiation. A
photon carries energy proportional to the radiation frequency but has zero rest mass.
Proton – a stable subatomic particle occurring in all atomic nuclei, with a positive electric
charge equal in magnitude to that of an electron, but of opposite sign.
Quantized - To limit the possible values of (a magnitude or quantity) to a discrete set of
values by quantum mechanical rules.
Quantum physics - Quantum physics is the study of the behavior
of matter and energy at the molecular, atomic, nuclear, and even smaller microscopic
levels. In the early 20th century, it was discovered that the laws that govern macroscopic
objects do not function the same in such small realms.
Radiation – energy that comes from a source and travels through some material or
through space. Light, heat and sound are types of radiation.
Radiowaves – an electromagnetic wave of a frequency between about 10 4 and 1011 or
1012 Hz, as used for long-distance communication.
Raman Spectroscopy – a spectroscopic technique used to observe vibrational, rotational,
and other low-frequency modes in a system. It relies on inelastic scattering, or Raman
scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near
ultraviolet range.
Reflectance – the measure of the proportion of light or other radiation striking a surface
that is reflected off it.
Sine Waves – a waveform that represents periodic oscillations in which the
amplitude of displacement at each point is proportional to the sine of the
phase angle of the displacement and that is visualized as a sine curve
Spectroscopy - The amount of energy emitted from stars is determined by measuring
their brightness or the amount of light they emit. This is called photometry. However, two
major developments expanded our understanding of the chemical make-up of stars. They
were:
a device that separates white light into
component colors called a spectrum.
chemical fingerprint in the spectrum.
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The two discoveries combined to produce a new field called spectroscopy, and allowed
astronomers to measure the chemical composition of stars for the first time.
Spectrophotometer – a device that measures either the amount of light reflected from a
sample object or the amount of light that is absorbed by the sample object.
Spectrum – an array of light waves or particles that are put in order by their physical
properties such as wavelength or mass. The band of colors or spectrum most often
produced when sunlight passes through a prism are red, orange, yellow, green, blue,
indigo, and violet.
Thermocouple – a thermoelectric device for measuring temperature, consisting of two
wires of different metals connected at two points, a voltage being developed between the
two junctions in proportion to the temperature difference.
Transmission spectrum – represents the transmission spectrum for a given
configuration and calculator. The radiant flux which passes through a filter divided by the
radiant flux incident upon it, for monochromatic light of a specified wavelength.
Ultraviolet – An invisible band of radiation at the upper end of the visible light spectrum.
With wavelengths from 10 to 400 nm, ultraviolet (UV) starts at the end of visible light and
ends at the beginning of X-rays. The primary source of ultraviolet light is the sun, and most
of the UV that reaches earth is in the lower-frequency, longer-wavelength Ultraviolet "A"
region (see below).
UV spectrophotometry – refers to absorption spectroscopy or reflectance spectroscopy
in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent
(near-UV and near-infrared [NIR]) ranges. The absorption or reflectance in the visible
range directly affects the perceived color of the chemicals involved. In this region of
the electromagnetic spectrum, molecules undergo electronic transitions. This technique is
complementary to fluorescence spectroscopy, in that fluorescence deals with transitions
from the excited state to the ground state, while absorption measures transitions from the
ground state to the excited state.
Valence electron – an electron that is associated with an atom, and that can participate
in the formation of a chemical bond; in a single covalent bond, both atoms in the bond
contribute one valence electron in order to form a shared pair. The presence of valence
electrons can determine the element's chemical properties and whether it may bond with
other elements: For a main group element, a valence electron can only be in the
outermost electron shell. In a transition metal, a valence electron can also be in an inner
shell.
Wavelength (λ) – In physics, the wavelength of a sinusoidal wave is the spatial period of
the wave—the distance over which the wave's shape repeats.
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Wavenumber – the spatial frequency of a wave, either in cycles per unit distance or
radians per unit distance. It can be envisaged as the number of waves that exist over a
specified distance (analogous to frequency being the number of cycles or radians per unit
time).
X-rays – p a form of electromagnetic radiation. Most X-rays have a wavelength in the
range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30petahertz to
30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to
100 keV. Portable X-ray units to gather forensic evidence such as bullet fragments
embedded in various materials. The portable X-ray machine can be used to examine
evidence on location with minimal disturbance or exfoliation.