From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Newsgroups: sci.chem
Subject: Re: Blue electrons?
Date: Fri, 02 Jul 1999 09:35:10 GMT

Roman A Kresinski <r.a.kresinski@staffs.ac.uk> wrote:
>Bruce Hamilton wrote:
>> The blue colour of liquid oxygen can be removed by passing the liquid
>> through activated silica gel, suggesting that it is caused by a small
>> equilibrium concentration of associated oxygen molecules. The blue
>> colour returns on standing after several hours.
>Liquid oxygen *is* associated oxygen molecules, if I should so insist.
>Can you clarify what you mean?

There are associations and associations...

The blue colour of liquid oxygen is believed to be due to a single photon
simultaneously elevating two electrons to excited states on two separate
ground state oxygen molecules. The absorption of the photon, combined with
1-3 vibrational quanta, creates a series of relatively-strong absorption peaks
in the red, yellow and green regions of the visible spectrum, thus resulting
in the perceived blue colour of the liquid. The temporary loss of the blue
colour after passing through an activated silica gel column, and the slow
return of colour, suggests the transition is relatively infrequent.

The transition can occur when two ground state oxygen molecules collide and
the resulting double molecule state ( which is not strongly bound ) contains
a singlet component. The three-body ( 2 oxygen and one photon ) process is
more likely to occur in the liquid  ( as more collisions will occur between
the oxygen molecules ), but it is an intrinsic property of the oxygen
molecule, and not a bulk property of the liquid.

         Bruce Hamilton