Silylidyne is a chemical substance occurring as a molecule found in stars and probably existing in interstellar space, or as a
monolayer on the surface of solid
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
. The SiH molecule is a
radical, and can be made experimentally by striking an
electric arc
An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. An ...
to silicon on a low pressure
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
gas.
Surface
As a surface layer, silicon hydrides form when the silicon is cleaned with hydrofluoric acid. These hydrides decompose to SiH when heated to 750 K.
Other ways to coat a silicon surface in hydrogen is via reaction with
atomic hydrogen
A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force. Atomic hydrogen constit ...
, or hot
silane
Silane is an inorganic compound with chemical formula, . It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Sila ...
.
[ A (111) crystal face will become covered in the pure monohydride, but other faces on a silicon crystal will also have the dihydride and trihydride groups.]
Group
The silylidyne group, not to be confused with silylidyne, is a ≡SiH group that is bonded with a triple bond. The hydrogen can be substituted by other groups to make a more generic family of silylidynes. It is known as a ligand on molybdenum.
Natural occurrence
Silylidyne in space was first noticed in sun spots in 1933. Later on it was found on the solar disk, photosphere, and in cool stars. Mira variable stars of type M or S may have emission lines of SiH. In even cooler brown dwarf
Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...
s and planets, SiH is not found, but instead silicon takes form as silicon monoxide
Silicon monoxide is the chemical compound with the formula SiO where silicon is present in the oxidation state +2. In the vapour phase, it is a diatomic molecule.
It has been detected in stellar objects and has been described as the most common o ...
at low pressures, and SiH4 at high pressures. Minute amounts of SiH as a transient species may be found in these bodies as SiO and SiH4 react with water.
Properties
The Si-H bond strength is 80 kcal/mol.[
]
Spectrum
The most prominent spectral band is due to A2Δ → X2Π transitions. Higher level excited states are the B2Σ− and C2Σ+, D2Δ, E2Σ+.[
The life time of the molecules in the A state is 530 nanoseconds. They decay to the X ground state.][
]
References
{{Reflist
Silanes