# What does propogation of wave packets mean?

1. Nov 19, 2012

### mycotheology

I'm reading an article about the photo induced ligand loss of metal carbonyl complexes at the moment and heres a bit I'm having trouble getting my head around:
Its the wavepacket part that I'm confused about. All I know is that a wavepacket is what you get when you combine multiple sine waves. I have no idea how this applies to an actual compound. Can anyone explain it in practical terms? When you shine light on the compound, the carbonyl ligands jump to higher energy states, similar to how electrons do. Where do wavepackets come into it?

2. Nov 19, 2012

### Dead Metheny

I am only an undergrad, so if someone more knowledgeable than me wants to illuminate us (or just me if I'm incorrect), I appreciate it.

My QM book discusses wave packets a little in the first few chapters. In QM, the particles you study are actually waves (not just point particles). Wave functions exist in a space (mathematically) such that they can be described as the sum of a bunch of different wave functions. These waves have probabilities of giving specific values when observed and the act of observation "collapses" the wave function such that subsequent measurements will yield the same result. On wave packets, my book more or less says: "A particle's velocity is not the speed of the individual ripples (phase velocity) but the speed of the 'wave packet' (group velocity)." I'm assuming, the wave packet refers to the sum of all of the wave functions that correspond to a "velocity measurement".

3. Nov 21, 2012

### mpv_plate

I'm not sure if this assumption is correct. Any quantum system has only one wave function. The wave function describes all possible configurations of the system. So a wave packet should not be a packet of wave functions, but a packet of waves of something else: for example electromagnetic waves. But correct me if I'm wrong.

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