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Red spectra of M stars are dominated by TiO(Titanium oxide) bands, which have become the primary means of establishing spectral types.see ApJ

Why is TiO special?

There should be much more Silicon elements than Titanium if we suppose the element abundance of M stars are similar to our sun.(Solar abundance is here). If similar,there should be much more SiO2 than TiO?

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    $\begingroup$ Doesn't mean that SiO2 is a stronger absorber. Optical depth is the integral over abundances and absorption strength after all. The solar abundances shouldn't be taken from some blog article, but rather from Asplund+2009 or similar. $\endgroup$ – AtmosphericPrisonEscape Apr 11 '17 at 22:20
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TiO is used as a sunscreen, it has high absorption and emittance rates and a high radiation potential. SiO2 is used for fiber optic cables and probably deflects and transmits photons a lot more, and it is very chemically inert, that's why the desert is made of quartz, it's all that is left after the rest has been weathered, it's orbitals are very stable and difficult to change. That's why silicon life forms probably don't exist, especially in a water world, they can't really bond with H and they absorb oxygen very tenaciously.

When a molecule absorbs a wavelength of light, an electron is excited from a full orbital into an empty anti-bonding orbital. Each jump takes energy from the light, and a big jump obviously needs more energy than a small one. Each wavelength of light has a particular energy associated with it. If that particular amount of energy is just right for making one of these energy jumps, then that wavelength will be absorbed - its energy will have been used in promoting an electron.

https://physics.stackexchange.com/questions/7437/why-glass-is-transparent

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  • $\begingroup$ Wow - first time I learn that silicon-based life forms aren't as easy. Great answer in general (although I'm slightly confused about the exact relation of the second paragraph to the first one.) $\endgroup$ – Helen - down with PCorrectness Apr 13 '17 at 14:54
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    $\begingroup$ Yes it's true, silicon is almost always a rock, and carbon based matter is similar to a room temperature lava that can change between millions of compounds, syrup, oil, acetone, starch, even carbon based meteorites contain 100ds of carbon compounds, carbond bonds with everything. and silicon makes only stones. The second paragraph was supposed to explain why glass electron orbitals don't absorb photons, it's difficult. here is info about silicon life-forms. biology.stackexchange.com/questions/53776/… $\endgroup$ – com.prehensible Apr 14 '17 at 16:58
  • $\begingroup$ Aren't the relative dissociation energies and the possibility of forming Ti- and Si-bearing molecules at particular temperatures the main issue? $\endgroup$ – Rob Jeffries Apr 18 '17 at 10:43
  • $\begingroup$ yes indeed. the dissociation energies aren't radically different. 662kj/mol for TiO and 798kj/mol for SiO2, which is one of the highest on the chart. a difference of 20% for dissociation energy. chemical inertness and dissociation energy are nearly the same? thorium oxide and N2 are the only ones that i found with higher energy at 850 and 950 kj/mol. It could also be that TiO is easier to make out from other mixed wavebands. $\endgroup$ – com.prehensible Apr 18 '17 at 11:09

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