Ok John, I'll bite:

It comes from the degeneracy = 2s+1 where s is the total spin angular 
momentum.
Having all paired electrons (i.e. as many up electrons as down) gives 
s=0 so the degeneracy is 1 = singlet.
If you have two unpaired up electrons the degeneracy is 2*(+1/2 + 1/2)+1 =3

Cheers Mark

 >
 >Luke Skywalker aside, what really confuses everyone is that none of 
these explanations states what is single in "singlet" and triple in 
"triplet".
 >
 >-- John J. Lemasters, MD, PhD
> LOL Mike
>
> But Luke skywalker only existed in a Galaxy far far away and long ago 
> even if he did have lots of possibilities in his mitochlorians  -or so 
> we are told...
>
> Cheers
>
> Ignatius, Mike wrote:
>> Boy, now I am really glad I didn't share my Luke Skywalker, avoid the
>> Dark Side/State analogy, that I use with students.  When Luke/Fluors are
>> activated, riled with hate, they are most vulnerable to going to the
>> dark side/state. 
>> Yoda: "But beware of the dark side. Anger, fear, aggression,
>> PHOTOTOXICITY, SIGNAL LOSS, the dark side of the Force are they."  
>> Luke: "Is the dark side stronger?" Yoda: "No, no, no. Quicker, 
>> easier, more seductive, HARDER TO PREVENT IN
>> LIVE CELLS." 
>> Anakin
>>
>> -----Original Message-----
>> From: Confocal Microscopy List [mailto:[log in to unmask]]
>> On Behalf Of Mark Cannell
>> Sent: Monday, February 16, 2009 1:03 PM
>> To: [log in to unmask]
>> Subject: Re: Photobleaching mechanism question
>>
>> While I am all for analogies to convey the basis of complicated 
>> processes to the ignorant, the analogy must be accurate. But in this 
>> case, if a _scientist_ asks about bleaching from the triplet state 
>> why does the explanation have to be dumbed down to such an 
>> (inaccurate) level?  Surely the basis of chemical reactions in terms 
>> of electrons and
>>
>> electron pairing should not be so unfamiliar after undergraduate physics
>>
>> and chemistry?
>>
>> A good explanation is given in Encyclopeda Britannica and should be 
>> within the grasp of most I think.
>>
>> http://www.britannica.com/EBchecked/topic/457736/photochemical-reaction/
>> 277509/Consequences-of-photoexcitation#ref=ref499215
>>
>> Even if you can't remember the simple reason for more rapid oxidation 
>> from the excited state (due to singlet oxygen production, I think, 
>> but probably other possibilities also exist in complex molecular 
>> systems), you point your undergraduates there rather than use 
>> horribly inaccurate analogies. If nothing else, a reason to learn 
>> this explanation is that it is the basis of life on earth as it 
>> explains how light can be harnessed to chemical reactions!
>>
>> Cheers Mark
>> P.S. Tobias, if you wonder why I object to your analogy it is because 
>> a power surge does not involve switching off the computer!!!!
>>
>>
>>  
>>> John,
>>>     From the non physicist's point of view the answer could go 
>>> something like this. If you have a power surge it can fry your 
>>> computer. But if your computer is not plugged into the mains then it 
>>> would take a very big power surge indeed to do the damage. A 
>>> molecule in the ground state can of course be damaged by free 
>>> radical attack but no more or less than other molecules. But once a 
>>> molecule has absorbed a photon then it is not in the ground state 
>>> any more. To continue my hoaky analogy, a chromophore in light is 
>>> like your computer plugged in to the mains.
>>>
>>>     Hope this helps. The physicists (and musicians) can go for the 
>>> triplets.
>>>
>>>     Tobias
>>>
>>>
>>>    
>>>> Hi Everyone,  this question follows on from a helpful discussion that
>>>>       
>>
>>  
>>>> we had about photobleaching back in November.  I have recently 
>>>> tried to explain to a group of colleagues about the mechanism of 
>>>> photobleaching.  The answer is based on the transition of molecules 
>>>> from the excited singlet state (S1) to the triplet state (T1) which 
>>>> is long-lived and therefore more susceptible to bleaching by free 
>>>> radicals (my entire discussion of this is below).
>>>>
>>>> My question that arises from my attempted answer is: why are 
>>>> excited molecules more susceptible to oxidative attack than ground 
>>>> state molecules.  I hope I'm not completely mucking up the 
>>>> mechanism here. Would the physicists out there please help.
>>>>
>>>> Thanks, John.
>>>>
>>>> The original answer: When excited, fluorophores generally 
>>>> transition from singlet ground state (S0) to singlet excited state 
>>>> (S1). Relaxation from S1 to S0 results in emission of heat and 
>>>> light (fluorescence). Lifetime in S1 is in the nano to pico second 
>>>> range and allows very little time for the excited molecule to 
>>>> interact with
>>>>       
>>
>>  
>>>> free radicals. Periodically, however, an excited molecule will do a 
>>>> transition from S1 to the triplet excited state (T1 - the physics 
>>>> of this is a bit difficult to understand). T1 is a very long-lived 
>>>> state
>>>>       
>>
>>  
>>>> - molecules can remain in T1 for up to the microsecond range - i.e. a
>>>>       
>>
>>  
>>>> thousand to a million times longer than for normal S1 state. It is 
>>>> during this long T1 state that molecules are attacked by free 
>>>> radicals and destroyed.
>>>>
>>>> -- 
>>>> Runions signature
>>>>
>>>> (Sent from my cra%#y non-Blackberry electronic device that still 
>>>> has wires)
>>>>
>>>>
>>>>
>>>> *********************************
>>>> John Runions, Ph.D.
>>>> School of Life Sciences
>>>> Oxford Brookes University
>>>> Oxford, UK
>>>> OX3 0BP
>>>>
>>>> email:  <mailto:[log in to unmask]>[log in to unmask]
>>>> phone: +44 (0) 1865 483 964
>>>>
>>>>
>>>>       
>> <http://www.brookes.ac.uk/lifesci/runions/HTMLpages/index.html%21>Runion
>> s'  
>>>> lab web site
>>>>
>>>>
>>>>
>>>> Visit <http://www.illuminatedcell.com/ER.html>The Illuminated Plant 
>>>> Cell dot com
>>>> Oxford Brookes Master's in
>>>>       
>> <http://www.brookes.ac.uk/studying/courses/postgraduate/2007/bmt>Bioimag
>> ing  
>>>> with Molecular Technology
>>>>       
>
>