I Rotational Orientation of Monatomic Gas: Angular Momentum Effects

[InkTide]

In other words, is there a rotational orientation of each atom in a monatomic gas (and corresponding rotational speed conserving angular momentum) that affects collisions, or does a substance need to have at least 2 atom particles to have the orientation/rotational ability to have particle motions and collision energies that are affected by/conserve the angular momentum of individual particles?

What about for spherical outer electron shells? Does that make a difference?

 

[sysprog]

Wouldn't the nucleus of each atom have angular momentum wrt its immediate neighbors?

 

[InkTide]

Wouldn't the nucleus of each atom have angular momentum wrt its immediate neighbors?

I'm not sure, especially given how compact the nucleus is and how structureless it is supposed to be. I've always been under the impression that nucleus-nucleus interactions are quite uncommon. If you mean in solids, I think it's no longer monatomic, and the interactions are still mostly between neighboring atoms' electron shells.

 

[jbriggs444]

I'm not sure, especially given how compact the nucleus is and how structureless it is supposed to be. I've always been under the impression that nucleus-nucleus interactions are quite uncommon. If you mean in solids, I think it's no longer monatomic, and the interactions are still mostly between neighboring atoms' electron shells.

As I understand it, it is not a physical question. It is a question about how you are defining angular momentum and its conservation.

A point-like body that is moving has non-zero angular momentum if you take your reference point to be somewhere other than at that body's center.

If you have one body over here and another body over there, they may each have zero angular momentum about their respective centers, but the system containing the two of them may have non-zero angular momentum about the system's center of momentum.

 

[InkTide]

As I understand it, it is not a physical question. It is a question about how you are defining angular momentum and its conservation.

A point-like body that is moving has non-zero angular momentum if you take your reference point to be somewhere other than at that body's center.

If you have one body over here and another body over there, they may each have zero angular momentum about their respective centers, but the system containing the two of them may have non-zero angular momentum about the system's center of momentum.

Does this allow point-like bodies to transmit angular momentum between each other through collisions? I'm also not sure the point-like body is the best analogy, because it's the nucleus that is point-like, but the electron cloud is more volume-like (not sure on that terminology) and that's what I believe is interacting in most collisions between atoms at low energies - perhaps this in and of itself is the answer I'm looking for, where the change in rotational energy of the atom after a collision is a function of the rotational energy of the colliding atom, the axis of that rotation, the rotational energy of the atom before the collision, the axis of that rotation, the relative orientations of the two axes (and therefore the angle at which the collision occurs relative to each atom's centers) to the center of each atom, and the linear speed of each atom prior to collision.

After doing some cursory research on basic kinetic molecular theories, I think the best way to describe it would be asking if isolated atoms of a monatomic material have rotational degrees of freedom - I think the answer is yes, they have them, but I'm still not sure if the electron cloud is non-point-like enough.

Now I'm wondering... does ionized hydrogen have rotational degrees of freedom? Can a proton have stable orientation and thus literal spin (as opposed to the quantum mechanical property)? If not... would proton collision with a rotating particle convert that particle's angular momentum into linear motion of the proton and vice versa? Kinetic molecular theory already establishes that vibration of molecular structure and rotation of molecules provide degrees of freedom and thus potential "modes" of thermal energy within a substance... what happens to the thermal behavior of matter when it has as few thermal energy modes as possible?

 

[jbriggs444]

Does this allow point-like bodies to transmit angular momentum between each other through collisions?

Yes, of course. If your reference point is 50 kilometers away, a pair of colliding particles will transmitted angular momentum by virtue of having transferred linear momentum.

It need not do anything to their intrinsic angular momentum, if any.

 

[hutchphd]

Kinetic molecular theory already establishes that vibration of molecular structure and rotation of molecules provide degrees of freedom and thus potential "modes" of thermal energy within a substance... what happens to the thermal behavior of matter when it has as few thermal energy modes as possible?

The issue for thermodynamics is interaction. If there is no coupling to the degrees of freedom in question, then they are not part of the system in question (and indeed will not,, by definition, ever be in thermal equilibrium). For the same reason we do not worry about the nuclear energy levels in an ideal gas at STP.
I note in passing that these thermodynamics questions are a prime instance where classicle mechanics is much more confusing than quantum mechanics. One is invariably led to counting questions about "how identical do particles need to be" or "what is ther energy threshold" using the classicle theory. In this case it would be "how spherical is perfectly spherical ?"

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