Bok Globule Barnard 68

Interstellar grains Sub-micron sizes

Interstellar grains Sub-micron sizes Cabonaceous and silicate material et ????

Interstellar grains Sub-micron sizes Cabonaceous and silicate material et ???? Who knows?

Gr  H…Gr  H…Gr…H  Gr…H2  H2  + Gr Charge transfer Exchange reaction 1 Exchange reaction 2 Exchange reaction 3

Gr  H…Gr  H…Gr…H  Gr…H2  H2  + Gr Charge transfer Exchange reaction 1 Exchange reaction 2 Exchange reaction 3

Gr  H…Gr  H…Gr…H  Gr…H2  H2  O+  O + Gr H H h Gr  H…Gr  H…Gr…H  Gr…H2  H2  O+  O + Gr Charge transfer Exchange reaction 1 Exchange reaction 2 Exchange reaction 3

Gr  H…Gr  H…Gr…H  Gr…H2  H2 + Gr H H h Gr  H…Gr  H…Gr…H  Gr…H2  H2 + Gr Charge transfer Exchange reaction 1 Exchange reaction 2 Exchange reaction 3

h photon or energy of reaction Localised heating

Critical Temperature Tc for lift-off for various molecules adsorbed on grains by van der Waals interactions Tc(K) H2 < 3 N2 13 CO 14 CH4 19 NH3 60 H2O 92

Harry Kroto 2004

Photo dissociation tPD = 103 AB + h  A + B Lifetimes (in yrs) Photo dissociation tPD = 103 AB + h  A + B 2-body collisions t2B = 103/n A + B  AB*  A + B Radiative association tRA = 109/n yrs A + B  AB*  AB + h Grain catalysis tGC = 109/n yrs A + B + Gr  AB + Gr 3 - body collision t3B = 1023/ n2 A + B + M  MAB  AB + M t(BIG U) = 1010 yrs n number of atoms or molecules per cm3 Harry Kroto 2004

Harry Kroto 2004

Harry Kroto 2004

Harry Kroto 2004