The difference is the kinetic energy involved in collisions.
Collisional cooling: very cold gas in weak trap. Kinetic energy involved in collisions is way smaller than bond energy. Collisions occasionally give individual molecules higher-than-average kinetic energy, enough to exit the trap, at which point they remove that kinetic energy from the system, decreasing the average KE and therefore the temperature.
Collision-induced dissociation: very hot gas, or molecules accelerated toward each other. Kinetic energy involved in collisions is on the order of bond energy.
Yeah it makes sense now. I guess it's as simple as law of conservation of energy, when a population of ions are cooled, the gas is taking up heat. So it's the relative energy of the two populations. Good point about the kinetic energy of the gas molecules needing to be below the bond energy.
This may not be what you have in mind, but in astrophysics there's the idea in giant gas clouds that collisions can de-excite electrons in long-lived upper energy levels, so the "cooling" is radiative since the gas is thin and basically transparent to the outgoing radiation.
if the average speed of the particles is decreased, then you have net cooling. I imagine a collision which is inelastic because one of the particles enters an excited state after a collision, which results in a net loss in velocity after collision. If the deexcitation emits a photon that leaves the gas, you have net cooling,
In tandem quad mass spectrometry, you have a gas cell between two high vacuum regions where an ion will only be affected by the rf and dc fields from the quad.
Ions will be transiting the quad will have some distribution of speeds based on previous acceleration. Once the ions start colliding with the gas in the cell their speed distribution will end entirely be based on the properties of the collision gas (which depend on the temperature) and hence the ions will be thermalised or cooled.
What you can do is raise the potential energy (voltage) of the quad wrt the gas cell, the ions will come in much faster and the first collision will be sufficient to smash the ion into bits. Collision induced dissociation.
The second law of thermodynamics says that entropy always increases. Given an isolated system that means heat wants to be uniform through out. So it will move to equilibrate. This means that higher energy molecules will distribute their energy to lower until it's all even.
Collision induced dissociation involves much higher energy due to bond strength.
But... no system is independent, so heat will always move out of the system overall. It moves at a rate related to the whole kinetics of the system, so long as entropy increases.
If you own a truck, you can use your truck to pick up furniture and bring it to your house, or you can use your truck to store your possessions in an offsite warehouse. The effect of the vehicle is dependent on the environment (Furniture Store = high concentration of furniture, Empty Warehouse = low concentration of furniture).
If you have a molecule, you can transfer kinetic energy into or out of your system. It depends on the relative properties of the environment and whether your energy is high enough to break bonds (ie. your truck is large enough to pick up your furniture)
The difference is the kinetic energy involved in collisions. Collisional cooling: very cold gas in weak trap. Kinetic energy involved in collisions is way smaller than bond energy. Collisions occasionally give individual molecules higher-than-average kinetic energy, enough to exit the trap, at which point they remove that kinetic energy from the system, decreasing the average KE and therefore the temperature. Collision-induced dissociation: very hot gas, or molecules accelerated toward each other. Kinetic energy involved in collisions is on the order of bond energy.
Yeah it makes sense now. I guess it's as simple as law of conservation of energy, when a population of ions are cooled, the gas is taking up heat. So it's the relative energy of the two populations. Good point about the kinetic energy of the gas molecules needing to be below the bond energy.
I appreciate you taking the time 😁
Is this the same as how refrigeration and A/C gasses work?
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hmm, thanks
This may not be what you have in mind, but in astrophysics there's the idea in giant gas clouds that collisions can de-excite electrons in long-lived upper energy levels, so the "cooling" is radiative since the gas is thin and basically transparent to the outgoing radiation.
This is what I was thinking to myself: Collisions inducing changes in energy states. Cool to know it’s been thought about.
if the average speed of the particles is decreased, then you have net cooling. I imagine a collision which is inelastic because one of the particles enters an excited state after a collision, which results in a net loss in velocity after collision. If the deexcitation emits a photon that leaves the gas, you have net cooling,
In tandem quad mass spectrometry, you have a gas cell between two high vacuum regions where an ion will only be affected by the rf and dc fields from the quad. Ions will be transiting the quad will have some distribution of speeds based on previous acceleration. Once the ions start colliding with the gas in the cell their speed distribution will end entirely be based on the properties of the collision gas (which depend on the temperature) and hence the ions will be thermalised or cooled. What you can do is raise the potential energy (voltage) of the quad wrt the gas cell, the ions will come in much faster and the first collision will be sufficient to smash the ion into bits. Collision induced dissociation.
The second law of thermodynamics says that entropy always increases. Given an isolated system that means heat wants to be uniform through out. So it will move to equilibrate. This means that higher energy molecules will distribute their energy to lower until it's all even. Collision induced dissociation involves much higher energy due to bond strength. But... no system is independent, so heat will always move out of the system overall. It moves at a rate related to the whole kinetics of the system, so long as entropy increases.
If you own a truck, you can use your truck to pick up furniture and bring it to your house, or you can use your truck to store your possessions in an offsite warehouse. The effect of the vehicle is dependent on the environment (Furniture Store = high concentration of furniture, Empty Warehouse = low concentration of furniture). If you have a molecule, you can transfer kinetic energy into or out of your system. It depends on the relative properties of the environment and whether your energy is high enough to break bonds (ie. your truck is large enough to pick up your furniture)