Why do molecules not fall apart under observation?

[The thinker]

Hello

I was just revising for my Quantum Mechanics A exam and was considering the 1D double well model of an H₂+ molecule. As I understand it Psi² is non zero between the wells and therefore there is some negative charge present to which the H+ nuclei are attracted resulting in a covalent bond.

But what happens when the electron is observed and found to be around either of the nuclei? i.e the wave fuction "collapses". Why does the molecule not split apart?

Thanks

 

[Bob S]

First, we need to understand the kinematics of the H2+ ion. Its binding energy is about 2.78 eV (please check this). This is comparable to the energy of a 450 nanometer wavelength photon. So a blue photon could (not will) dissociate an isolated H2+ ion. Macroscopic laws like conservation of energy would prevent dissociation of an isolated ion when the photons are less than 2.78 eV (or longer than 450 nm). The electron cannot be "observed" without disturbing it (per the Uncertainty Principle). The wave function of the 3 particles is nothing more than a probability function; not the kind like rolling snake eyes with two dice. It just implies a fuzzy area where the electron's wave function is (but not where the electron is), but nothing about what its binding energy to either or both protons is at any given time. What can be said is that UV photons could dissociate it by photoelectron emission, but the probability would be based on detailed calculations of the density of final states, and that green light >= 500 nanometers long cannot dissociate it, because of conservation laws.

 

[Entropia]

for your question. This is a very interesting topic in quantum mechanics and has been studied extensively by scientists. The short answer is that the wave function collapse does not physically affect the position of the electron or the nuclei. The wave function only represents the probability of finding the electron at a certain position, and its collapse simply means that we have obtained a measurement of its position.

In the case of the H2+ molecule, the covalent bond between the two nuclei is a result of the attractive force between the negative charge of the electron and the positive charge of the nuclei. This bond is strong enough to keep the nuclei together even when the electron is observed to be around one of the nuclei.

Additionally, the act of observation itself does not cause any physical disturbance to the molecule. The observer's measurement of the electron's position does not physically interact with the molecule and therefore does not cause it to fall apart.

Furthermore, the collapse of the wave function is a probabilistic event, meaning that there is still a chance that the electron can be found around the other nucleus. This is known as quantum tunneling and is a phenomenon that allows particles to pass through potential barriers, such as the bond between the nuclei in the H2+ molecule.

In conclusion, the covalent bond between the nuclei in a molecule is strong enough to keep them together even when the electron is observed to be around one of the nuclei. The collapse of the wave function does not physically affect the position of the electron or the nuclei, and quantum tunneling allows for the possibility of the electron being found around either of the nuclei. I hope this helps clarify your understanding. Good luck on your exam!