# Is the energy of an orbital dependent on temperature?

In the Schrodinger Equation's solution for electron orbital energy levels of the hydrogen atom there is no temperature dependency. $$E_n = - \frac{m_{\text{e}} \, e^4}{8 \, \epsilon_0^2 \, h^2 \, n^2}$$

Maybe this is due to ignoring the effects of temperature when deriving the Hamiltonian. No sources I have seen mention any assumptions about temperature. Are electron orbital energies dependent on temperature in spite of this common equation?

If you have hydrogen gas heated to near ionization then it should take less than 13.6 eV to remove an electron.

For some reason Im having trouble confirming any of this thru google. Is it 13.6 eV no matter what temperature it is or is there a temperature dependency?

• Dec 3, 2020 at 4:37
• Temperature is undefined for a single atom. Dec 3, 2020 at 9:55
• @my2cts not for a classical atom, but single atom quantum states with well-defined temperatures do exist. Of course, these are not eigenfunctions of the hamiltonian Dec 3, 2020 at 13:54
• @Tristan What is a classical atom? How can a single atom state exist that is not an eigenfunction? Do you mean an incoherent state described by a density matrix? Dec 3, 2020 at 20:21
• true, classical atom doesn't really make sense. My point was mostly that whilst classically the temperature of a single object doesn't make sense, in a quantum system it can Dec 4, 2020 at 9:41

## 4 Answers

Maybe this is due to ignoring the effects of temperature when deriving the Hamiltonian.

How are you defining heat at the quantum level? The Schrodinger equation describes how objects behave at the quantum level and heat describes a form energy which is transferred between objects of different temperatures. Temperature is a macroscopic quantity and not microscopic. The equation above describes the energy of electrons in a specific shell and these electrons can change energy by the absorption or emission of photons, and photons do not possess temperature.

No sources I have seen mention any assumptions about temperature.

For exactly those reasons.

Are electron orbital energies dependent on temperature in spite of this common equation?

No they are not.

If you have hydrogen gas heated to near ionization then it should take less than 13.6 eV to remove an electron.

No. Heating hydrogen will not cause the absorption of photons which is needed to ionise hydrogen (other methods for ionisation of atoms exist, but I’m speaking in the context of this question). Moreover, the hydrogen will be ionised upon the absorption of photon with this energy and not any less. This is the crux of the term energy and other quantities are quantised at a microscopic level which gave rise to quantum mechanics.

Is it 13.6 eV no matter what temperature it is or is there a temperature dependency?

Once again temperature is not relevant here. For ionisation to occur, a photon must be absorbed (there are other ways to ionise atoms too). So to answer your question, there is no such dependence.

• Maybe it would be instructive to mention that the stability of spectra for a given atom is what allows us to measure a doppler shift from stars moving away or towards us. astro.ucla.edu/~wright/doppler.htm Dec 3, 2020 at 8:42
• It is because the spectrum of a given atom, is independent of temperature that the doppler shift of the spectrum can be used to measure the velocity of the star.. If the spectrum could be variable then it could not be used for such a measurement. Dec 3, 2020 at 9:03
• If you heat up hydrogen such that kT >> ground state energy, you can in fact effect the spectra (you will of course will ionize the atoms into a plasma). Dec 4, 2020 at 9:07
• It might help to also add that temperature is a property of an ensemble, reflecting the translational energy of particles, not the "internal" energy of electron states. Dec 4, 2020 at 22:39

In addition to @Dr jh's answer, I would like to add that the effect of temperature on the spectra of atoms is part of what is known as as Doppler broadening of the lines.

In atomic physics, Doppler broadening is the broadening of spectral lines due to the Doppler effect caused by a distribution of velocities of atoms or molecules. Different velocities of the emitting particles result in different Doppler shifts, the cumulative effect of which is the line broadening. This resulting line profile is known as a Doppler profile. A particular case is the thermal Doppler broadening due to the thermal motion of the particles. Then, the broadening depends only on the frequency of the spectral line, the mass of the emitting particles, and their temperature, and therefore can be used for inferring the temperature of an emitting body.

Italics mine

• Btw, this was indeed instructive and a great response showing that temperature is independent of temperature via an empirical example which is independent of any opinions. Plus I didnt know of this very cool phenomenon. Dec 13, 2020 at 17:34

I think this question belies a misunderstanding of the nature of temperature.

Temperature is not an input to fundamental physical laws, it is something that comes out of the physical laws when applied to a large number of objects. There is no explicit temperature in the Schrödinger equation for a hydrogen atom. The concept of temperature only emerges when you consider the Schrödinger equation for a large number of hydrogen atoms that can exchange energy with each other.

The Schrödinger equation (or Newton's laws or Maxwell's equations) establish the ground rules for how atoms and molecules (or any other objects) behave. However, it's usually difficult to work out what these rules predict for anything more than simple systems. The point of statistical mechanics is to predict the average behavior of a large number of such simple systems under the constraints provided by the ground rules (fundamental physical laws). Temperature is a concept that emerges from the statistics of large number of degrees of freedom that can exchange energy. Again, it is not an input to the Schrödinger equation or Newton's laws, but a consequence of them!

Temperature is a macroscopic property. Individual atoms don't have temperature. An analogy would be income inequality: it makes sense to ask how much income inequality a country or state or city has, but it doesn't make sense to ask how much income inequality a single person has. A simplified version of what temperature is is that it is a measure of how much difference between velocities there is between atoms. Just as it doesn't make sense to ask how much difference between incomes there is when you're talking about a single person, it doesn't make sense to ask how much difference in velocities there is if you're talking about a single atom.

If anything, heating a gas will increase the ionization energy. The ionization energy is given for the frame of reference of the atom. If an atom is moving at a high speed relative to us, then the ionization energy in our frame energy is increased.

It's not clear what you mean by "heated to near ionization". According to this, 13.6 eV corresponds to 158 thousand degrees Kelvin. So if you were to heat hydrogen to that temperature, you would see ionization from the collisions. But that doesn't mean the ionization energy is decreased, it means the energy is met.