Astrochemistry#


Introduction

Much of this chemistry occurs in β€œdense” interstellar clouds and protostellar disks surrounding forming stars because these environments have higher relative densities and more benign radiation fields than in stellar ejectae or the diffuse interstellar medium.

In this section we will focus on the chemistry within Molecular clouds.

Review:

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Plan


  • Summary

Notes

Page

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  • Reviewed: ❌

  • Updated: 15/02/2023

Introduction#

The ISM has always been considered too hostile of an environment for the formation of molecules.

  • Intrerstellar Radiation Field (ISRF) that have UV wavelength < 200 nm dissociates any molecules that may have formed (atom density also very low in the ISM).

However ISM is not homogeneous and it’s physical and chemical composition can vary widely.

Note

Should I include ISM environments here

Think so

ISM#

Note

include

Most of the molecules discovered have been observed within molecular clouds - coldest densest regions of the ISM.

Dust grains shield those clouds from ISRF. Hence molecules within the clouds are not dissociated

Basic Chemistry in Cold Cores#

β€£ Gas-phase chemistry #

β€£ Grain-surface chemistry #

From Cold core to PPD#

How much of the initial material is processed

../../_images/Herbst_dust_warm_2009.png

Fig. 17 Taken from []#

Photoprocessing#

[]: VUV spectroscopy, morphology of various molecular ices

Complex Organic Molecule#

Abbreviated COMs.

Precursors#

Methanol#

Note

Insert methanol image + Observation spectra

Interstellar CH3OH forms exclusively in the condensed phase on the surfaces of dust grains in dense molecular clouds, via successive hydrogenation of CO. High variation in abundance of solid methanol are observed in the ISM (between 5% and 30% relative to H2O). Hard to determine because of overlapping feature with water and silicates.
../../_images/Methanol-3D-balls.png
  • ISM abundance from observation spectra
  • Laboratory studies of mixture

Pre-biotique molecules in space#

Prebiotic molecules are defined as molecules that are thought to be involved in the processesleading to the origin of life.

Below are a few of them:

Of the interstellar prebiotic molecules, many were first detected toward Sgr B

Nucleobase synthesis#

in interstellar ices

  • [] (❌ to read)

  • []

Reactivity#

Surface reaction#

  • [] (❌ to read)