Thread: Destroying a molecule with a laser?

Hello everyone,

Would it be possible to destroy a molecule with a laser at a precise frequency?

I was thinking maybe that could be used to destroy the CO2 and CH4 molecules in the atmosphere. The lasers could possibly be mounted on flying drones that would use solar energy to stay in the air for days and to provide the energy for the laser.

Nic.

This wouldn't really help as hitting CO2 or CH4 with a laser would produce molecules and radicals (CO and CH3 mainly) that feature in the natural atmospheric oxidation of hydrocarbons, you would just be speeding up photochemical ozone production (tropospheric ozone as well as being a component of smog is also a greenhouse gas...). If you are going to speculate along these lines you really need to understand what products you will form and what will happen to them in the atmosphere, section 2 in this link (Tropospheric Chemistry) is a good starting point.

Originally Posted by PhDemon

This wouldn't really help as hitting CO2 or CH4 with a laser would produce molecules and radicals (CO and CH3 mainly) that feature in the natural atmospheric oxidation of hydrocarbons, you would just be speeding up photochemical ozone production (tropospheric ozone as well as being a component of smog is also a greenhouse gas...). If you are going to speculate along these lines you really need to understand what products you will form and what will happen to them in the atmosphere, section 2 in this link (Tropospheric Chemistry) is a good starting point.

Ok. Wouldn't it be possible to destroy the CO and CH3 molecules too with other laser frequencies?

Thank you for the link, I'll read at it as soon as I can.

Originally Posted by Nic321

Originally Posted by PhDemon

This wouldn't really help as hitting CO2 or CH4 with a laser would produce molecules and radicals (CO and CH3 mainly) that feature in the natural atmospheric oxidation of hydrocarbons, you would just be speeding up photochemical ozone production (tropospheric ozone as well as being a component of smog is also a greenhouse gas...). If you are going to speculate along these lines you really need to understand what products you will form and what will happen to them in the atmosphere, section 2 in this link (Tropospheric Chemistry) is a good starting point.

Ok. Wouldn't it be possible to destroy the CO and CH3 molecules too with other laser frequencies?

Thank you for the link, I'll read at it as soon as I can.

To reiterate what PhDemon has said, you always have to ask yourself is what the products would be of these "destroyed" molecules. They will not just turn into nothing. They will turn into either fragments of molecules or atoms (or ions, possibly). So unstable atoms or part-molecules, still containing carbon, would be formed. These would look for a "partner" in order to form a stable molecule again. What do you suppose they might choose as partners?

Yes I see the problem indeed.

I read the document PhDemon posted, it is too copknow how the molecules would recombine. From what I understand several molecules, like hydroxyl, play an important role in the life of certain molecules, like methane, and these molécules have different concentrations in different parts of the atmosphere. Perhaps there would be a way to decrease the half-life of CO2 or methane by acting on hydroxyl, etc with a laser, I don't know.

From the document I see that CH4 can become ultimately CH2O or CH3O2. Do these molecule pose a problem? (GHG something else )


I am under the impression after all that a laser might not be very well suited, because it is too directionnal. Maybe a more omni-directional type of antenna would enable to hit more molecules.

Out of curiosity, do you think it would work to break molecules in the atmosphere ( without considering the recombination that would happen after )? What would be the frequency for CH4 and CO2 for instance? And how precise does the frequency have to be?

Formaldehyde and peroxy radicals are all tied up in the photochemical cycles that happen in the atmosphere, changing their concentrations can have a massive impact on the chemistry of the atmosphere so yes I would say they are a problem... (the information in the link I gave you is an introduction to this), there are whole books and hundreds of research articles on thus subject (I've written a few!). The minimum frequency required would be that corresponding to the energy of the chemical bond you want to break...

Originally Posted by PhDemon

Formaldehyde and peroxy radicals are all tied up in the photochemical cycles that happen in the atmosphere, changing their concentrations can have a massive impact on the chemistry of the atmosphere so yes I would say they are a problem... (the information in the link I gave you is an introduction to this), there are whole books and hundreds of research articles on thus subject (I've written a few!). The minimum frequency required would be that corresponding to the energy of the chemical bond you want to break...

So a photon with a given frequency is going to break any molecule which requires a certain minimum frequency to be broken? So it is not really possible to chose to break a particular molecule?

Broadly speaking yes, although it is not that simple, you have to consider the photolysis cross-section of the molecule at that frequency and the quantum yield for the process...

Ah ok. So perhaps it might be possible but it would lead to all sorts of other problems with the remaining molecule.

Also, wouldn't it be possible to have like 2 superimposed lasers, to force a particular recombination? one laser breaks the CH4, the other breaks another particular molecule in exactly the same beam, and they recombine immediately the way we want.

Maybe in theory (I've heard of similar things in the lab in low pressure pulsed laser experiments) but in practice the atmosphere is too dense for your idea to work in practice...

Also, the energy required to construct, install, power and operate the lasers would - intuitively - generate more CO₂ than was converted by the process.

Ok it wouldn't work.

All those stories about global warming are worrying, in particular the possibility of abrupt methane release from the arctic sea bed. Kind of scary...

Thank you for the explanations PhDemon.

If there is the political will we can address all the problems of AGW. Energy conservation, renewable energy and carbon capture, in combination, can provide a solution. The problem is the lack of sufficient political will. But kudos for thinking outside of the box in search of a solution.

Originally Posted by John Galt

If there is the political will we can address all the problems of AGW. Energy conservation, renewable energy and carbon capture, in combination, can provide a solution. The problem is the lack of sufficient political will. But kudos for thinking outside of the box in search of a solution.

Thanks John.

I read news regularly on the subject of AGW and it is very worrying. In particular the issue of methane releases from the arctic sea bed which seems to be accelerating.

I hope scientists will find a solution to this problem otherwise...

Nic.

Originally Posted by Nic321

Originally Posted by John Galt

If there is the political will we can address all the problems of AGW. Energy conservation, renewable energy and carbon capture, in combination, can provide a solution. The problem is the lack of sufficient political will. But kudos for thinking outside of the box in search of a solution.

Thanks John.

I read news regularly on the subject of AGW and it is very worrying. In particular the issue of methane releases from the arctic sea bed which seems to be accelerating.

I hope scientists will find a solution to this problem otherwise...

Nic.

The solution is to convince China and India to stop polluting. Best of luck.

The solution is to convince China and India to stop polluting. Best of luck.

Yes. The population also continues to increase rapidly in other parts of the world. Some people are convinced we are already doomed. Maybe it is naive to think that we can avoid a catastrophic abrupt global warming at this point.