Instrumental

Which type of scattering results in a longer wavelength than the incident light?

Stokes: photon with lower energy and longer wavelength

Which type of scattering is the strongest?

Rayleigh

Which of these properties must change for a mode to be Raman active?

Polarizability: it cannot be constant when passing through the equilibrium position if a mode is to be Raman active

Sulphur hexafluoride (SF6) is centrosymmetric. What statements is true?

SF6 has an inversion center, obeys the rules of mutual exclusion, and IR modes will be Raman Inactive

What technique can be used to give a stronger signal than normal Raman Spectroscopy?

Resonance Raman: Increases Raman scattering. Fourier uses interference and ROA compares polarization light

How many possible orientations doe spin 1/2 nuclei have when they are located in an applied magnetic field?

2

When radiation energy is absorbed by a spin 1/2 nucleus in a magnetic field, what happens?

The angle of precession "flips" so that the magnetic moment of the nucleus opposes the applied field.

What is the name given to the relaxation process due to an interaction between an excited nucleus and the magnetic fields caused by nuclei in molecules moving around in the sample

spin - lattice relaxation

In FT-NMR, how are nuclei excited?

by an intense pulse of r.f. radiation which contains a wide range of frequencies

Why is it advantageous to record many FID signals from the same sample and then add them together?

To increase sensitivity

What is meant by "rotating frame of reference?"

That we imagine the laboratory itself is rotating at the Larmor frequency. From this viewpoint, individual magnetic moment vectors are fixed in space.

Is Free Induction Decay Signal recorded in the time domain or the frequency domain?

Time Domain

Describe the mechanism of the production of an MNN Auger electron.

An M electron is ejected by X-radiation or by a beam of electrons. An N electron then descends to the M orbital while ejecting a second N electron as an Auger electron.

Describe how it is possible to distinguish between XPS peaks and Auger electron peaks.

Auger and XPS peaks can be distinguished by comparing spectra obtained with two different sources (such as an Al and Mg tube). Auger peaks are unaffected by the change in source whereas XPS peaks are affected by the change.

Scanning Electron Microscopy (SEM) images are produced by collecting the emitted electrons on a cathode ray tube display. Calculate linear magnification achievable in the SEM image displayed on the CRT screen (100 mm x 100 mm) if the electron beam is made to scan a raster 10 um x 10 um on a sample.

100 mm / 10 um

100mm x 1000 = 100000 um

100000 um/10um = 10000 um

In SEM higher spatial resolution can be achieved by analyzing

Secondary Electrons (inelastic interactions)

What parts of the instrument are common to all of these: electron microprobe, SEM, TEM? What components are the same for all three?

Electron gun and electromagnetic lenses.

One unique property of mass spectrometry is that the formular for a specific ion or fragment can be determined by knowing its mass to the fourth or fifth decimal place. This technique, accurate mass determination, is based on the fact that only a very specific combination of atoms may result in a specific mass and is therefore very useful at identifying unknown compounds. In order to determine the mass if an unknown analyte while discriminating it s molecular ion from a potential interfering species with a very similar mass requires a mass spectrometer with a very high . . .

Resolution (resolving power) in the tens of thousands or more

Quadrupole mass analyzers are the most common in inexpensive, benchtop GC-MS instruments. A primary reason for this is . . .

GC-MS need fast-scanning capabilities to determine the mass spectrum of the analyte at multiple points as a chromatographic peak elutes.

Mass analyzers that normally use a Fourier transform to deconvolute data collected from the analyte ions of interest are usually based on . . .

ion cyclotron resonance. Ions trapped in plates

In the _________ mass analyzer, analytes are ionized, and the resulting ions are held in a radio frequency fields between end-cap and ring electrodes. This analyzer is commonly used as a chromatographic detector.

ion trap

Electron Ionization sources are the most common, standard ionization sources in modern, benchtop gas chromatograph-mass spectrometers (GC-MS). The reason for this is . . .

EI sources work well for analytes with masses < 1000 amu. Most molecules that can be separated by gas chromatography would be expected to have smaller masses.

In gaseous ionization, the sample is first volatilized (by heating if necessary) and then transmitted to the ionization area for ion formation. The advantage of gaseous sources are their simplicity and speed (no need to use probe and wait for prob area to be pumped out). TRUE or FALSE?

TRUE

In a desorption source, a probe is used and ionization takes place directly from the condensed form of the sample. The advantage of desorption ionization is that it can be applied to high molecular weight and thermally unstable samples. TRUE or FALSE?

TRUE

The most fragmentation and thus the most complex spectra are encountered with . . .

electron ionization: lots of fragmentation.

The simplest spectra is produced with . . .

field desorption (FD)

What is true when comparing electron ionization to chemical ionization sources for mass spectrometry?

Chemical ionization sources often result in a !molecular ion (M+) peak! in the mass spectrum. !Ejection of an electron from the analyte due to electrostatic repulsion! from source generated electrons is what causes ionization in the EI source.

For large biomolecules such as polypeptides, proteins and others having masses greater than 10,000 amu, what two sources are commonly used to increase the mass range of quadrupole mass analyzers

Electrospray Ionization and Fast Atom Bombardment

In the Chemical Ionization source, reagent gases such as methane can react to form positively charged ions that are used to then ionize the sample. For example, methane (CH4) can produce CH5+ reagent ions in the source. Through which processes are single charge and sometimes protonated ions are produced?

Proton transfer and hydride transfer.

When using the matrix assisted laser desorption ionization (MALDI) source, the analyte _______ has a much greater influence on the volatilization and ionization than EI, CI or other sources

matrix

What types of mass spectrometers are used in ICPMS?

Quadrupole, time-of-flight mass spectrometers, and double-focusing mass spectrometers.

The most common type of mass spectrometer used in atomic mass spectrometry is the quadrupole mass analyzer. TRUE or FALSE?

TRUE

The quadrupole mass spectrometer is analogous to which component of optical instruments?

variable-band filter

Quadrupole: Separation of ions of different masses occurs by . . .

varying the dc and ac potential simultaneously.

In time-of-flight mass spec ions are accelerated periodically into a field-free drift tube. Their velocity in the tube is determined by their mass to charge ration so that they arrive at a detector at different times depending upon their mass. The heavier ion arrive at the detector earlier than the lighter ones. TRUE or FALSE?

FALSE

What funciton does the ICP torch have in ICPMS

Atomization and Ionization

Why has ICPMS become an important and widely used analytical method?

high sensitivity, high selectivity, and good precision for determining most elements in the periodic table. Ar+ has highest ionization energy so most elements can be ionized when colliding with Ar+

In NMR spectroscopy FID stands for

Free Induction Decay

Estimate the relative number of protons in the higher and lower magnetic states (N2/N1) when a sample is placed in 300 MHz (7.05 T) NMR instrument at room temperature (25C)

1

What is the name given to the relaxation process due to an interaction between neighboring nuclei having identical precession rates but different magnetic quantum states?

Transverse, or spin - spin relaxation. Population doesn't change but the lifespan does decrease

What is the name given to the relaxation that arises from complex magnetic fields that are generated by the rotational and vibrational motions of the host of other nuclei making up a sample?

Longitudinal, or spin - lattice, relaxation.

NMR parameter which is measured in parts per million using an internal reference (usually TMS)

chemical shift

NMR parameter that measures the spacing in frequency units between the peaks produced by spin-spin splitting

coupling constant

NMR parameter that measures the degree to which circulation of electrons around the nucleus reduce (or sometimes increase) the magnetic field felt by the nucleus.

shielding constant.