Lot Spectroscopy

What is a Spin-Lock Field in NMR Spectroscopy?

Moreover, if you can, I would like to know which information I can extract from the sequent experiments: NOESY, ROESY, TOCSY.

Thanks a lot to anyone who can help me =D.

Nuclear magnetic resonance, or NMR as it is abbreviated by scientists, is a phenomenon which occurs when the nuclei of certain atoms are immersed in a static magnetic field and exposed to a second oscillating magnetic field. Some nuclei experience this phenomenon, and others do not, dependent upon whether they possess a property called spin.

Spectroscopy is the study of the interaction of electromagnetic radiation with matter. Nuclear magnetic resonance spectroscopy is the use of the NMR phenomenon to study physical, chemical, and biological properties of matter. As a consequence, NMR spectroscopy finds applications in several areas of science. NMR spectroscopy is routinely used by chemists to study chemical structure using simple one-dimensional techniques. Two-dimensional techniques are used to determine the structure of more complicated molecules. These techniques are replacing x-ray crystallography for the determination of protein structure. Time domain NMR spectroscopic techniques are used to probe molecular dynamics in solutions. Solid state NMR spectroscopy is used to determine the molecular structure of solids. Other scientists have developed NMR methods of measuring diffusion coefficients.

Field Lock
In order to produce a high resolution NMR spectrum of a sample, especially one which requires signal averaging or phase cycling, you need to have a temporally constant and spatially homogeneous magnetic field. Consistency of the Bo field over time will be discussed here; homogeneity will be discussed in the next section of this chapter. The field strength might vary over time due to aging of the magnet, movement of metal objects near the magnet, and temperature fluctuations. Here is an example of a one line NMR spectrum of cyclohexane recorded while the Bo magnetic field was drifting a very significant amount. The field lock can compensate for these variations.
The field lock is a separate NMR spectrometer within your spectrometer. This spectrometer is typically tuned to the deuterium NMR resonance frequency. It constantly monitors the resonance frequency of the deuterium signal and makes minor changes in the Bo magnetic field to keep the resonance frequency constant. The deuterium signal comes from the deuterium solvent used to prepare the sample. The animation window contains plots of the deuterium resonance lock frequency, the small additional magnetic field used to correct the lock frequency, and the resultant Bo field as a function of time while the magnetic field is drifting. The lock frequency plot displays the frequency without correction. In reality, this frequency would be kept constant by the application of the lock field which offsets the drift.

On most NMR spectrometers the deuterium lock serves a second function. It provides the =0 reference. The resonance frequency of the deuterium signal in many lock solvents is well known. Therefore the difference in resonance frequency of the lock solvent and TMS is also known. As a consequence, TMS does not need to be added to the sample to set =0; the spectrometer can use the lock frequency to calculate =0.

i hope this helps

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Astronomy - spectroscopy - 2/3

Age of earth? and those irritating polonium halos?

Hi guys

Polonium 218, exists for only a few seconds before it decays.

That's why there is not a lot of it about naturally,

however, in granite rock, polonium halos of isotope 218 have been discovered embedded within.

Now here in lies the problem

while people would estimate granite to be millions of years old
and polonium 218 exists for only a few seconds

how on earth do visible polonium halos get embedded in granite rock which is supposed to be millions of years old?

the polonium should have long decayed, but it's clearly visible to the eye and to scientific tests, such as spectroscopy.

One possible answer, is that they were created at the same time,

to those who dispute this, i would like to know what you think

link is provided below:

http://www.ichthus.info/Creation-Evidence/Polonium-Halos/intro.html

http://www.halos.com/

From what I read it seems to make sense. However, as for all the answers, these people are only looking in science, and not in their history. Throughout history there have been stories of dragons all over the world. In the 1700's, the word dragon was still used, only later on did they begin to use dinosaur. Have you ever heard of the 'Nasca' or 'Ica' stones?
These stones have dinosaurs carved on them. Some of the dinosaurs have circular patterens on them. Just a few years ago, fozzilized dinosaur skin was found, with surprise, circular markings. Now these stones were carved at about the time of christ and were found again in 1571. How would these people from only 2000 years ago know what dinosaurs looked like unless the dinosaurs where actually there? We have two choices, either there where still dinosaurs around or aliens came from outer space with a time machine, and zapped a whole pile of dinosaurs to that current time. Tell me, which is easier to believe? Now if you just happen to have one, grab an antique dictionary from the 1700's. Look up the word dragon. You will find that it says, a rare, though still living animal. So much for the theory that dinosaurs only lived millions of years ago.