the physics and chemistry...1 the physics and chemistry on the surface of cosmic dust grains alexey...

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THE PHYSICS AND CHEMISTRY

ON THE SURFACE OF COSMIC DUST GRAINS

Alexey Potapov Laboratory Astrophysics Group of the Max Planck Institute for Astronomy

2Credit: Lund observatory

The whole sky (by eyes)


The whole sky (by eyes)

“a lot of stars and black holes” (Jules Verne)


Molecular clouds

Credit: Nielbock et al. 2012

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Origin of life

Earth

Prebiotic molecules

Interstellar medium

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Credit: Burke & Brown 2010

Structure of dust/ice grains

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HRTEM image of silicate grains (real surface area is unknown) Inset: carbon grains on a KBr substrate (nominal surface area is 1 cm2)

High porosity Large surface


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Cold condensation of dust in dense clouds


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Comet 67P (credit: ESA)


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Dust is physically mixed with ice!

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Thermal desorption of H2O ice

A – integrated band intensity T – temperature v0 – pre-exponential factor = 1012 b – heating rate = 1 K/min N – number of molecules i – desorption order E – desorption energy

dA/dT = v0.1/b.Ni.e-E/RT

H2O

H2O+carbon grains

H2O H2O + carbon grains

Potapov A. et al., ApJ, 2018, 865, 58

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Thermal desorption of H2O ice

Correction factor of 400!

Ice coverage of dust grains in the ISM:1018 molecule cm-2 – 1000 ML / 400 = 2.5 ML

HRTEM image of silicate grains (real surface area is unknown) Inset: carbon grains on a KBr substrate (nominal surface area is 1 cm2)

H2O (130 nm, 400 ML):desorption order = 0 – multilayer desorption

H2O (130 nm, 400 ML) + carbon grains:desorption order = 1 – monolayer desorption

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Cosmic dust grains

Huge number of studies

from simple molecules to amino acids

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- Direct participation of functional groups and atoms in surface reactions

Threefold catalytic effect- A place where molecules can rapidly diffuse and react

- A third body to dissipate the energy released in exothermic bond formations

- Lowering the activation barriers of reactions

Role of dust grains in the chemistry on their surfaces

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Direct participation of dust

A handful of studies

CO2 in H2O ice covering hydrogenated carbon grains by ion irradiation (Mennella et al., 2004)

CO and CO2 in H2O ice covering hydrogenated carbon grains by UV irradiation (Mennella et al., 2006)

CO2 in O2 ice covering atomic carbon foils by UV irradiation (Fulvio et al., 2012)

CO2 in H2O ice covering atomic carbon foils by proton irradiation (Raut et al., 2012)

CO and CO2 in H2O ice covering hydrogenated carbon grains by proton irradiation (Sabri et al., 2015)

CO and CO2 in H2O ice covering graphite films by UV irradiation (Shi et al., 2015)

Formation of CO and CO2

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LabAstro, Jena MONARIS, Paris

+

Amorphous hydrogenated fullerene-like carbon grains

Sample - fixed on a copper mirror at 10 K

High vacuum chamber (10−9 mbar)

Bombardment – 30 minutes, 1.8×1020 atoms cm-2

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Difference IR spectrum before and after O/H bombardment of carbon grains

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A new route of molecules formation in the ISM: grain surface processes

Potapov A., …, Krim L., ApJ, 2017, 846, 131

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Catalytic effect of dust

Some studies

H2 on crystalline silicate films (Pirronello et al., 1997)

H2O on amorphous silicate films (Jing et al., 2011)

H2O on amorphous silicate films (He and Vidali, 2014)

H2 on amorphous silicate grains (Gavilan et al., 2014)

…

Formation of H2 and H2O

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FTIR spectrometer

Closed-cycle helium cryostat

Turbopump

FTIR detector

Quadrupole MassSpectrometer

Turbopump

Sample lock

Pressure gauge

Pressure gauge

Gate valve

UV source

Annealing chamber

Rotatable flange

Ion + Non-Evaporable-Getter pump

QMS

FTIR spectrometer

Gas inlet

Gas inlet

UV source

FTIR detector

Cryostat

Sample holder

Ion pump

INterStelar Ice Dust Experiment (INSIDE)

CO2 + 2NH3 → NH4+NH2COO-

Potapov A. et al., ApJ, 2019, 880, 12

UHV chamber (10-11 mbar)

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IR spectra taken after the deposition of a NH3:CO2 4:1 mixture on carbon grains at 15 K and after 4 hours of the reaction at 80 K

Time dependences of the NH4+NH2COO- column density

evolved from isothermal kinetic experiments at 80 K

* NH4+NH2COO-

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Dependence of the reaction rate coefficients of the CO2 + 2NH3 → NH4+NH2COO-

reaction on the ice thickness for various surfaces

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Potapov A., Theule P., et al., ApJL, 2019, 878, L20

Monolayer

Multilayer

Dependence of the reaction rate coefficients of the CO2 + 2NH3 → NH4+NH2COO-

reaction on the ice thickness for various surfaces

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- An increased diffusion rate of species

- A formation of an intermediate weakly bound CO2‒NH3 complex that helps to overcome the reaction barrier

- Lowering of the activation barrier of the reaction

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- An increased diffusion rate of species?

- A formation of an intermediate weakly bound CO2‒NH3 complex that helps to overcome the reaction barrier

- Lowering of the activation barrier of the reaction

Potapov A. et al., to be submitted

60 65 70 75 80

1,0x10-4

2,0x10-4

3,0x10-4

4,0x10-4

5,0x10-4

6,0x10-4

7,0x10-4

carbon KBr

k (s

-1)

Temperature (K)

0,012 0,013 0,014 0,015 0,016 0,017

-8,8

-8,6

-8,4

-8,2

-8,0

-7,8

-7,6

-7,4

ln(k

)1/T

carbon (activation energy 115 K)

KBr (activation energy 340 K)

CO2

NH3

Hea t

Dust gr ains

CO2

CO2

NH3

NH3

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Role of dust grains in the chemistry on their surfaces

C

Atom bombardment (H + O)

C

C

C

C

CC

C

C

CHydrogenation reactions (as a good example)

H + N CH3NH2

CO2

H + O CH3OH

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4000 3500 3000 2500 2000 1500 1000

0,92

0,96

1,00

O-H stretchingO-H bending

Tra

nsm

issi

on

Wavenumber, cm-1

H2O 200 K

MgSiO3/H

2O

200 K

Si-O stretching

Trapping of water in silicates

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Potapov A. et al., ApJ, 2018, 861, 84 and to be submitted

4000 3500 3000 2500 2000 1500 1000

0,92

0,96

1,00

O-H stretchingO-H bending

Tra

nsm

issi

on

Wavenumber, cm-1

H2O 200 K

MgSiO3/H

2O

200 K

Si-O stretching


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Trapped water can survive the transition from cold star-forming regions to protoplanetary disks and stay in silicates in the terrestrial planet zone

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Cheers, Xander!

the physics and chemistry...1 the physics and chemistry on the surface of cosmic dust grains alexey...

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