Raman Vocab 5

Question 1

occurs when two or more particles collide without any loss of energy

Answer 1

Elastic scattering

Question 2

both conservation of momentum and conservation of kinetic energy are observed. This means that while the directions of the particles may change, the total kinetic energy of the system is always conserved

Answer 2

elastic collision

Question 3

An elastic scattering process that occurs when photons of monochromatic radiation
with energy strikes a molecule, and the scattered radiation contains photons of the same energy as that of the incident radiation

Answer 3

rayleigh scattering

Question 4

occurs when the collision of two or more particles is accompanied by a change in the internal state of the particles. the energy of the incident particles is not conserved; rather, some of the incident energy is gained or lost

Answer 4

inelastic scattering

Question 5

part of the kinetic energy is changed to some other form of energy in the collision

Answer 5

inelastic collision

Question 6

An inelastic scattering process that occurs when photons of monochromatic radiation with energy strike a molecule, and the scattered radiation contains photons of different energies
than that of the incident radiation. if change in E corresponding to ṽv lies in 0-3000 cm-1, then ṽv represents a change in the rotational/vibrational energy of the molecule, giving rise to a spectrum

Answer 6

raman scattering

Question 7

The process by which the molecule gains energy during the inelastic Raman scattering collisions at the expense of the incident photons, resulting in Raman scattered photons of lower energy than that of the incident photons

Answer 7

stokes raman scattering

Question 8

The process by which the photon gains energy during the inelastic Raman scattering collisions at the expense of the molecule, resulting in Raman scattered photons of higher energy than that of the incident photons,

Answer 8

anti-stokes raman scattering

Question 9

The characterization of the energies of Raman vibrational modes by the magnitude of their wavenumber shift from the incident excitation energy, rather than their absolute
wavenumber. The use of wavenumber shifts to specify Raman vibrational energies insures that these bands are always plotted at identical energies, independent of the particular laser wavelength used in the experiment

Answer 9

raman wavenumber shift

Question 10

mathematical relationship between two points that possesses both magnitude and direction

Answer 10

vector

Question 11

The vector product of the distance separating two charges of equal magnitude and the magnitude of the charge

Answer 11

permanent dipole moment

Question 12

magnitude of permanent dipole moment reflects

Answer 12

strength of polarity of bond

Question 13

Result of the intense external electric and magnetic fields produced by the electromagnetic radiation of a laser inducing a separation of the electrons and protons in a molecule

Answer 13

induced dipole moment

Question 14

The degree of deformation of the electron cloud of a molecule induced by an incident
electric field

Answer 14

polarizability

Question 15

a 3 x 3 matrix that establishes a linear relationship between vectors.

Answer 15

tensor

Question 16

the ratio of the intensity of the Raman scattered light polarized perpendicular to the X-Y plane to that of the scattered light polarized plane parallel to X-Y

Answer 16

depolarization ratio

Question 17

Raman vibration in which depolarization ratio = 0 .

Answer 17

completely polarized vibrational mode

Question 18

raman vibration in which 0 < ρ < 3/4.

Answer 18

polarized vibrational mode

Question 19

results in highly polarized raman bands

Answer 19

totally symmetric vibrations

Question 20

raman vibration in which ρ = 3/4

Answer 20

depolarized vibrational mode

Question 21

all antisymmetrical raman vibrations are

Answer 21

depolarized

Question 22

In a molecule that possesses a center of symmetry, molecular vibrations that are symmetric with regards to the center of symmetry are forbidden in the infrared spectrum, whereas molecular vibrations that are antisymmetric to the center of symmetry are forbidden in the Raman spectrum.

Answer 22

Rule of Mutual Exclusion

Question 23

the lasing medium is continuously pumped and continuously emits light. The emission can occur in a single resonator mode, i.e. single-frequency operation, or on multiple modes.

Answer 23

continuous wave laser

Question 24

the property of any laser where the optical power appears in a pulse train of a specified time duration at a specified repetition rate

Answer 24

pulsed lasers

Question 25

Common gas lasers used in Raman spectroscopy, often based on Ar+ or Kr+; generally high power consumption lasers as input energy must be used to first ionize the Ar or Kr atoms and then excite to high energy states for population inversion and lasing; CW or pulsed operation possible; high output power (10 W) possible; supports multiple important lasing wavelengths in blue, green and red spectral regions

Answer 25

ion lasers

Question 26

Common gas laser uses neutral atoms, not ions; low power consumption, high reliability; generally low output power (<100 mW); supports only a single red lasing wavelength, 632.8 nm.

Answer 26

He-Ne laser

Question 27

Solid state, doped semiconductors that function as a light-emitting diode, converting current into light. Highly efficient, with low power and cooling requirements, and a useful power range (0.1 – 1 W). Wide wavelength range available, primarily in the near-infrared region (670 – 860 nm). Most commonly used for Raman is 785 nm. Disadvantages include high divergence of the output beam, and multi-mode output that can lead to wavelength drift.

Answer 27

diode lasers

Question 28

A general class of instruments that collects, spectrally disperses, and reimages an optical signal. Widely used dispersive instrument used to optically isolate single wavelengths from a polychromatic source.

Answer 28

monochromator

Question 29

An instrument used for dispersing electromagnetic radiation into its component spectrum. Refers to a two-dimensional device in which the separated wavelengths are imaged simultaneously along a horizontal axis at the output focal plane. Can also refer to a dispersive instrument, e.g. a Czerny-Turner monochromator, in which the single element detector at the exit slit is replaced by a multichannel detector that records large segments of the spectrum at once in the focal plane of the instrument

Answer 29

spectrograph

Question 30

A spectrograph containing a single grating for dispersion. Single grating instruments are common, simple, and high throughput (f/# 4, T ~0.4) optical instruments; however, they have relatively poor laser line and stray light rejection capabilities (~10-5). Must be pair with a separate Rayleigh rejection filter for use in Raman spectroscopy.

Answer 30

single spectrograph

Question 31

A spectrograph in which two single grating monochromators are combined in series with a common intermediate slit. Uses “additive dispersion” in which the light is dispersed twice, leading to excellent stray light rejection properties (10-10 – 10-12). Disadvantage is relatively low throughput (f/# 8, T ~0.1); double spectrographs are also not as useful with multichannel detectors due to their high dispersion resulting in reduced spectral coverage.

Answer 31

double spectrograph

Question 32

A spectrograph with 3 gratings and 4 slits that is used for very high stray light rejection (10-12) and observation of small Raman shifts from the Rayleigh line (<100 cm-1). First two gratings act in “subtractive dispersion” mode as a specialized double pre-monochromator filter to efficiently eliminate the Rayleigh scattered light. Dispersion is done by the last (3rd) grating. Major disadvantage is very low overall optical throughput (f/# 6, T <0.1).

Answer 32

triple spectrograph

Question 33

Spectrograph based on a design that uses holographic transmission gratings coupled with holographic Raman notch filters. Very high optical throughput (f/# 1.8, T ~0.5) with very good stray light rejection (~10-11). Disadvantages are fixed wavelength and fixed resolution.

Answer 33

holographic spectrograph

Question 34

detector used in the UV/Vis spectral region that acts like a series of phototubes. The cathode and anode are biased by 400 – 2500 mV and separated by a series of intermediate dynodes, each progressively more positively biased, which provides an electron multiplication cascade. Overall: 106 amplification possible; however, have relatively low quantum efficiency (~1 – 10%).

Answer 34

Photomultiplier Tube

Question 35

multichannel detector used in UV/Vis/NIR spectral regions. Solid-state sensor with integrated circuit technology. Photons strike MOS-on-p-type Si capacitor; electron charge stored in wells; serial readout destroys accumulated charge; high quantum efficiency (90%) possible.

Answer 35

Charge Couple Device

Question 36

The averaging of signal over adjacent pixels, or even whole columns, in a multichannel detector to increase signal strength.

Answer 36

binning

Question 37

A two-grating tunable bandpass filter in which the 1st and 2nd stages have opposing dispersion directions; no net dispersion occurs, but this design strongly discriminates against the laser wavelength. Can be used as an effective Rayleigh laser line rejection filter.

Answer 37

subtractive pre-monochromator

Question 38

A multilayer dielectric or holographic filter that blocks the Rayleigh scattered wavelength while allowing both the Stokes and Anti-Stokes Raman shifted wavelengths to pass; notch filters have relatively narrow (5 – 10 nm) band widths with high absorbance (>106) at the design wavelength to block the Rayleigh scattered light; the notch filter will reject a high fraction of the Rayleigh wavelength but transmit wavelengths just a few nm’s away.

Answer 38

raman notch filters

Question 39

A multilayer dielectric filter with high absorbance (>106) at the laser wavelength to block Rayleigh scattered radiation, but also acts as a long pass filter to allow Stokes Raman shifted wavelengths to pass; generally provide the narrowest transition from high absorbance to high transmission for observation of Raman bands extremely close to the laser line. Also available as short pass filters to allow observation of Anti-Stokes Raman wavelengths.

Answer 39

raman edge filters