EÐL620M / Life in the Universe Astrophysics – chemistry – Biology – earth-/planetary sciences Atoms - chemical bond Carbon chemical bond Atoms and molecules in space; Informations derived from spectroscopy Molecules in the universe; Existance and formation Interactions between light and matter ; photochemistry, photoionization, photofragmentation Thermochemistry in the Universe Biochemistry

H + H H2 A + B AB

Et U Ekin Ekin U U Ekin A + B A - B rAB

Et DE U Ekin A + B C*, (EC+DE) C, (EC) A - B rAB

A + B Et A - B rAB A + B + C AB + C

+ A + B + C A-B + C A + B + ? A-B + ? A + B + M(s) A-B + M(s) EAB EM + DE -

A + B + M(s) A-B + M(s) M(s) e.g. M(S) = “dust” = particles in space

“dust” / particles act as catalysis for molecular formation “dust”: ca. 1% of compounds in ISM “dust”: typically 0.1 – 1 mm

“dust” ? Cold clouds Solid states compounds

C Atom + atom Molecule M(s) but: Atom + molecule Molecules Molecule + molecule Molecules e.g. Exchange reactions:

C Atom + atom Molecule M(s) but: Atom + molecule Molecules Molecule + molecule Molecules e.g.: Exchange reaction: e.g.: A + H3CB ACH3 + B

C Atom + atom Molecule M(s) En: Atom + molecule Molecules Molecule + molecule Molecules e.g.: Addition: H2C=CH2 + AB H2AC-CH2B

Molecules in MC 12 different Atoms Most common: H, C, N & O : “CHON”

GMC / hot cores: »106 molec/cm3 T » 102 (<103)K T » 10-20 K T » 300 K ISM: »1 molec/cm3 Earth/surface: »1019 molec/cm3

Collisions between particles needed for reactions Collision frequency A + B / ZAB A + A / ZAA (no. of collisions per sec per volume unit): ZAA µ size/ dA2 ZAA µ velocity A = v(T, mA) ZAB µ [A] [B] ZAA µ [A]2 d

T, mA const.: Z´AA = [A]2 GMC / hot cores: »106 molec/cm3 Z´AA = 1012 Z´AA = 1 Z´AA = 1038 ISM: »1 molec/cm3 Earth/surface: »1019 molec/cm3 -and in GMC / ISM: A = H (?)

A + M ??? M1 + M2 ??? A + B C + D

A + M ??? M1 + M2 ??? A + B C + D

A + M ??? M1 + M2 ??? A + B C + D

A + M ??? M1 + M2 ??? A + B C + D Rate µ ZAB Rate µ f (No. of molecules with enough energy to exceed activation energy) Rate µ f ZAB

A + M ??? M1 + M2 ??? A + B C + D

A + M ??? M1 + M2 ??? A + B C + D Cross section = s = <d>2p d But ions:

But ions: A+ + B C + D + F µ 1/r2 - + +

But Ions: A+ + B C + D + - + +

+ + But ions: A+ + B C + D Collision frequency much larger Ion reactions very important in space

+ A + M ??? M1 + M2 ??? A + B C + D Ions: Collision cross section = s >> <d>2p d

A + M ??? M1 + M2 ??? A + B C + D Rate µ ZAB Rate µ f (No. of molecules with enough energy to exceed activation energy) Rate µ f ZAB

T Ea Orka, E Reaction coordinate A + B -> C + D f = exp(-Ea/kBT)

H2C=CH2 + AB H2AC-CH2B Ea

H2C=CH2 + AB H2AC-CH2B Ea Catalysis effect

T Ea Orka, E Reaction coordinate A + B -> C + D f = exp(-Ea/kBT)

Ea Small Energy, E Reaction coordinate Radicals A. .B H. .OH Cl. .CH3 -reactivity determined by electron pairing A. + .B A:B + .OH H:OH Cl. + .CH3 Cl:CH3 Unpaired electrons enhance reactivity Energy, E Reaction coordinate A. + .B A:B Ea Small f =exp(-Ea/kBT) » 1