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== Spin in piezochemical mechanosynthesis ==

[https://en.wikipedia.org/wiki/Intersystem_crossing Intersystem_crossing]: <br>
This can lead to the problem in [[piezochemical mechanosynthesis]] that when pressing [[moieties]] together too fast to hard, <br>
the reaction can actually lock up and slow down rather than speed up. {{wikitodo|check details}} <br>
This is one of the listed points in: [[Piezochemical mechanosynthesis#Surprising facts]]

Spin flips in tool-tips (to create an anti-parallel bonding singlet state) can be influenced by <br>
nearby massive atoms with high spin orbit coupling. <br>
{{wikitodo|find out how that is supposed to be working}}

{{todo|answer questions below – eventually explain and illustrate results}} <br>
'''Perhaps open questions are:'''
* Which heavy elements to use for speeding up reactions by speeding up inter system crossing?
* Which geometries to place these atoms on the tooltips ideally? (proximity, orientation)
* How important is this: How big is the effect and how do different reactions vary?

'''Related:''' 
* [[Organic anorganic gemstone interface]]
[[Nanosystems]] (from glossary) about '''Inter system crossing ...'''
* ... and energy dissipation, 224
* ... in pi-bond torion, 231
* ... radical coupling, 215
* ... rates of, 197, 216
* ... and reaction reliability, 210
* (also noted on page 235 top)

== Some other maybe interesting related trivia ==

=== Electron spins ===

Oxygen has as its unexcited state the [https://en.wikipedia.org/wiki/Triplet_state triplet state] with unpaired parallel electron spins 
(meaning it is a stable diradical). This is quite unusual.
The excited state of oxygen is [https://en.wikipedia.org/wiki/Singlet_oxygen singlet oxygen] with paired antiparallel spins. 
Singlet oxygen is quite metastable leading to fluorescence (red colored) <br>

----

Ortohelium is heliums ground state (with necessarily paired antiparallel spins). <br>
Parahelium with unpaired parallel spins (and necessarily one electron in the 2s shell) <br>
is surprisingly metastable (despite being excited by a whopping 19,8 eV). There is a "forbidden" state transition. <br>
(Wikipedia: [https://en.wikipedia.org/wiki/Helium_atom Helium atom])

=== Nuclear spins ===

A rare case where nuclear spins have a huge (physical) effect are the 
[https://en.wikipedia.org/wiki/Spin_isomers_of_hydrogen nuclear spin isomers of hydrogen].

Nuclear spins usually have only minor effect on physical and chemical properties. <br>
But they are very useful for analytic (and in the future maybe computation) purposes.

== Related ==

* [[Mechanically stable electronically excited states]]
* Polyaromatic pigments, F-centers in gemstones, ...See: [[color emulation]]