On the problem of band spread in the UV spectrometry

Doberman1 · Aug 2, 2015

On the point of confusing the speed with frequency think about it this way. If the emitter is travelling towards the observer, the point of origin of each successive wave is closer to the observer, hence it will take less time to reach the observer than for the wave which preceded it. So from the perspective of the observer, the waves do seem compressed as if they were sound. However, from the perspective of the waves themselves, no such compression occurs do to the velocity boost they received from the moving emitter. You can also think of the emitter moving along together with an affixed wavetrain. The observer will detect only the peaks and valleys on this wavetrain. Because of the velocity boost provided by the emitter, the peaks and valleys will stream faster past the observer.

Doberman1 · Aug 2, 2015

The whole effect may also provide an illusion of space stretching, since in the case of a receding emitter, waves are constantly added to the wavetrain.

10A · Aug 2, 2015

Doberman1 said: ↑

On the point of confusing the speed with frequency think about it this way. If the emitter is travelling towards the observer, the point of origin of each successive wave is closer to the observer, hence it will take less time to reach the observer than for the wave which preceded it.
Click to expand...

Of course it will take less time, if light is traveling at C and the emitter is 299,792 km away it will take 1 second to reach me. If the emitter is 149,896 km away, it will take 1/2 a second to reach me (in a vacuum). The speed of light hasn't changed.

Doberman1 said: ↑

. So from the perspective of the observer, the waves do seem compressed as if they were sound. However, from the perspective of the waves themselves, no such compression occurs do to the velocity boost they received from the moving emitter. You can also think of the emitter moving along together with an affixed wavetrain. The observer will detect only the peaks and valleys on this wavetrain. Because of the velocity boost provided by the emitter, the peaks and valleys will stream faster past the observer.
Click to expand...

There is no boost to the speed of light from the moving emitter. The speed of light remains the same. Yes the frequency increases, which is what you're trying to describe, that doesn't change the speed of light.

Maybe an analogy will help. You can picture it like a freight train. The train is traveling at 20 meters/second. The freight cars are 20 meters long. Every second you (standing still) count 1 car go by. Another freight train goes by at the same speed, 20 meters/sec. However the cars on this train are 10 meters long. The train is traveling at the same speed but now you count 2 cars every second. Both trains are traveling at the same speed, but their cars per second (frequency) and length of cars (wavelength) are different.

Brett Nortje · Aug 3, 2015

Doberman1 said: ↑

Because the UV wavelengths are so much shorter than infrared, the superimposition of vibration and rotation of the molecules is much more pronounced with the result that bands in the UV spectra are very much broader and spread out than in an infrared spectrum that features distinctly sharp lines. In other words, the distance displaced by the molecule during its rotational and vibrational cycles is sufficient to affect UV wavelengths to exhibit a significant frequency spread, but has a barely perceivable frequency spread in the infrared range due to longer wavelengths involved.
if the Einsteins General Theory of Relativity was correct and light propagation occurred according with the relativist laws of time frames of reference, such frequency spread then should not take place, since the light emitted by molecules at a given specific frequency should reach us always and regardless of that molecules vibration or rotation, with that same precise frequency. What happens instead from our velocity frame of reference, is when, during its rotational cycle, the molecule recedes from us, its apparent wavelength increases while the frequency decreases, and vice versa when the molecule vibrates in the direction towards us. Thats what causes the frequency spread. From the molecules velocity frame of reference however, the frequency and wavelength of the light emitted never changes.
To demonstrate a common misconception regarding these differences in resolution in molecular spectra which seems to vary with the wavelengths of radiation emitted, I would like to quote from Roberts, Gilbert, Rodewall, Wingrove page 119:
The diffusiveness of the spectrum is a consequence of the fact that electronic transitions can occur from a variety of vibrational and rotational levels of the ground electronic state into a number of different such levels of the excited electronic state. Thus, although the transitions themselves are quantized and therefore should appear as sharp lines, the fact that closely spaced vibrational-rotational levels give rise to closely spaced lines causes coalescence of the discrete absorptions into a band envelope to produce the broad bands observed experimentally.
The problem with this interpretation lies in the statement that electronic transitions can occur from vibrational and rotational levels of the ground electronic state into a number of different such levels. The phenomenon is not caused by electrons jumping between the ground and excited orbits, but instead what seems to take place is for the distance displaced by the atom in a molecule during its vibrational and rotational cycles to superimpose itself against the wavelength of a constant parameter specific for a given molecule, given off by electrically or electromagnetically excited electrons.

Let's say you have a vibrating molecule relative to you - a stationary observer. This molecule gives off a beacon at regular time intervals - longer intervals if it's an "infrared" beacon, and shorter intervals if it sports a "UV" beacon. Then of course the quasi-Doppler rules apply. When the molecule is accelerating towards you, the acceleration in the velocity of the molecule relative towards you will add to the velocity of the beacon signal's wavefront and you will get a higher frequency signal. If the same molecule accelerates away from you then the acceleration will subtract from the velocity of the beacon signal and each subsequent beacon wavefront will travel slower towards you and hence the time interval between the beacons will increase. Alternatively, a true Doppler effect may apply where the beacon wavefront always travels at the same velocity towards you, but the beacon wavefronts will reach you more frequently if the molecule is accelerating towards you and less frequently if the molecule accelerates away from you. Either way, this is what creates the frequency spread in the spectrum of the molecule. But then, and this is the key, this spread can be more - or less pronounced depending on what light we are dealing with. The effect will be more pronounced if the molecule gives off radiation in the ultraviolet range because the increase and decrease in time interval between individual beacons given off which results from the max and min velocity of the molecule relative to you, is a much greater fraction of the time interval between the individual beacon signals in the "UV" range than it is in the "IR" range. Hence the vibration of a molecule will induce a much greater frequency spread in the UV light than in the IR light of a vibrating molecule.

This perceived effect in a vacuum however may operate in conjunction not with the true Doppler rules which apply to sound waves which in turn are distortions in the air medium, and here the sound waves always travel at a constant speed relative to the air medium, not relative to you or the emitter. You just may happen to be stationary relative to the air medium. The light in the vacuum however knows no medium. Hence Einstein would be vindicated if the frequency spread results from the difference in min and max velocity of the vibrating molecule, where the wavefronts always travel with the same velocity but are only pushed closer and further apart, and proven wrong if the spread results from the difference in min and max acceleration of the molecule relative to you.
Click to expand...

If you want to have artificial light as powerful as natural light, then you need to add power to the light you are emitting.

If what you are talking about is about traveling at the speed of light, this can be accomplished by building a hull out of nitrogen four.

What effects are you looking for?

- - - Updated - - -

Doberman1 said: ↑

The whole effect may also provide an illusion of space stretching, since in the case of a receding emitter, waves are constantly added to the wavetrain.
Click to expand...

I would say they have mass, as they get pushed by those behind them, so, i guess you are right, but, what on earth is the goal of all this speculation?

Log in or Sign up

On the problem of band spread in the UV spectrometry

Doberman1 New Member

Doberman1 New Member

10A Chief Deplorable Past Donor

Brett Nortje Well-Known Member

Share This Page

Log in or Sign up

On the problem of band spread in the UV spectrometry

Doberman1 New Member

Doberman1 New Member

10A Chief Deplorable Past Donor

Brett Nortje Well-Known Member

Share This Page

Useful Searches