# How would one collapse a molecular wavefunction?

1. Apr 1, 2009

### exmachina

In NMR for molecules, one can collapse the nuclear spin wavefunction $$\psi_{nucspin}$$ by applying the magnetic moment operator $$\mu$$. That is, $$\psi_{nucspin}$$ becomes one of the eigenfunctions of $$\mu$$. This physically corresponds to hitting the nuclei with photons in the radiofrequency range.

In the Born-Oppenheimer approximation:
$$\Psi_{molecule}\approx \psi_{electron} \psi_{nuclear}$$

Clearly $$\psi_{nucspin}$$ is one component of $$\psi_{nuclear}$$, there are other components of $$\psi_{nuclear}$$ such as $$\psi_{nucrotation},\psi_{nucvibration}$$, etc.

That is,
$$\psi_{nuclear}=f( \psi_{nucrotation},\psi_{nucvibration},\psi_{nucspin})$$

So which operators would I use to collapse $$\psi_{nucrotation}$$? What frequency of light would I need?

How do I even go about calculating something like this?

2. Apr 7, 2010

### Hellabyte

Definitely not an expert on NMR, but I would possibly think that you would just send photons of the same energy as the energy gap between vibrational states. Isn't this the only frequency at which the photon will interact with the molecules vibrational states and therefore cause a wave function collapse?