Astrochemistry

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Introduction

Much of this chemistry occurs in “dense” 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

• Introduction
  • Atomic structure
• IR Spectroscopy

• Summary

Notes

To Do

• Think about coherent plan

• Implement

Colaboration

Presentation

Page

• Status:

• 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

‣ Gas-phase chemistry

‣ Grain-surface chemistry

From Cold core to PPD

How much of the initial material is processed

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.

• 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:

Glycoaldehyde

Fig. 18 C₂H₄O₂ - Source

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Discovery: []

Observations: CDMS Database

Formation Pathways: Insert articles

Comments: Formation mediated by interstellar amorphous ice: a computational study - arxiv

Glycolonitrile

Fig. 19 HOCH₂CN - Source

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Discovery: []

Observations: CDMS Database

Formation Pathways: Insert articles

Comments:

Aminoacetonitrile

Fig. 20 NCCH₂NH₂ - Source

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Discovery: []

Observations: CDMS Database

Formation Pathways: Insert articles

Comments: Precursor of glycine

Formamide

Fig. 21 CH₃NO - Source

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Discovery: Implement source

Observations: CDMS Database

Formation Pathways: Insert articles

Comments:

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

Nucleobase synthesis

in interstellar ices

• [] (❌ to read)

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Reactivity

Surface reaction

• [] (❌ to read)