Meijer Astrochem Flashcards

Question

what are the problems associated with spectroscopy in space?

Answer 1

Lifetime, pressure and line broadening Doppler effect Line of sight Resolution

Answer 2

The transitions are naturally broadened by the lifetime of excited state

Answer 3

When two molecules collide, there is a shift in energy which changes the width of a transition

Answer 4

collisons between atoms are infrequent and if pressure broadening present then this indicates dense regions of space.

Answer 5

Doppler effect

Answer 6

Everything in space is governed by gravity there is no limit on M1 and M2 Inverse relationship with R means that there is always an interaction even at long distances

Answer 7

2Ek + Eg = 0 lots of mass required for star formation To prevent star collapsing Ek > -0.5 Delta G

Answer 8

1. Stars are formed from molecular clouds that contain interstellar matter such as h, He and Li. 2. Star formation starts when the denser regions of the cloud being to collapse under gravity 3. Gravity attracts matter in to form a core of material 4. Temperature increases and the gravitational attraction is balanced out by the heat of expansion. 5. A prostar formed which emits IR radiation 6. Envelope of material around core continues to shower mass into prostar and get collapse again 7. As it contracts the core become optically thick, IR no longer able to escape and temp increases 8. Temp becomes high enough that get dissociation of hydrogen and eventually ionisation 9. Bare protons can collide with enough energy to induce nuclear fusion 10. Solar wind developing which shakes off dust jacket and star begins to form

Answer 9

Mass of star achieves a critical mass (jeans mass)

Answer 10

1. Fusion of two protons 2. Proton capture 3. He fusion source of energy for young stars

Answer 11

Loss of hydrogen means temp and pressure decreases, and star collapses. He starts to burn. Triple He collision to give carbon - 12. it is not dense enough for C-12 nuclei to collide

Answer 12

Core of star begins to collapse again, raising the temp until nuclear reactions involving He start. C-12 + 4He - O-16 and gamma alpha capture continues in a similar way to give Si and S once you have 12C - CNO cycle where 13C, 12N, 14N and 15O undergo alpha capture to produce other elements

Answer 13

where the mass is less than the mass of the sun He burning only core contracts and shell expands

Answer 14

``` Mass is greater than the sun alpha capture C/O burning gives Ca Si burning gives Fe (dense stars) Further collapse after S/O burning ```

Answer 15

Density matter of cloud collapses and core consist of neutrons

Answer 16

stars unstable and blow off large amounts of matter. this generates shock waves which induce the collapse of clouds and start new star formation

Answer 17

Heavy elements

Answer 18

Once population inversion between the ground and excited state occurs then a photon with the same frequency of the transition can interact and stimulate emission from excited state Radiation around the star is likely to have a wavelength to stimulate the transition. When stimulated emission occurs in the microwave region it is said to be a MASER

Answer 19

No permanent dipole so there is no rotation or vibration spectrum. Electronic spectrum blocked by UV

Answer 20

21 cm line

Answer 21

Proton and electron have spin, so there are two configurations. Collisions with other species populate the excited state, transition to the GS is forbidden so has a long lifetime. This transitions produces a wavelenght of 21 cm

Answer 22

Absorption features in the spectra of stars. They are found in the front and and around stars.

Answer 23

Molecules have large moments of inertia and excited Hydrogen could be a carrier for bands.

Answer 24

Density plot, indicates where there is most interaction with ISM

Answer 25

Molecular Hydrogen and Co emission of a photon reduces the energy and therefore T. These are very abundant in ISM

Answer 26

Abundance - conc of species may not be high enough to be detected. Could be unstable and have short lifetimes. Radiation can degrade them. Molecules can collide with fast moving stars and be ionised Shock waves can destroy molecules when stars formed.

Answer 27

emanate from vibrational transitions in the ground state OH masers are in the outermost parts of compact water regions and ionised spheres around hot and young stars.

Answer 28

Matter and raditation that exists in the space between the star systems and the galaxy

Answer 29

H,C,N,O so dominate molecular formation

Answer 30

Diffuse ISM - 100K bare grains GMCs - dense region, 10k and diverse and complicated chemistry. Star formation occurs Circumstellar medium - young stars have high proton flux. Molecules photodissociated and photoionised Proton dominated regions - photolysis

Answer 31

Optical extinction - IS dust can scatter or absorb light from distant stars. A photon collide with a particle which can result in the photon changing direction and being removed from line of sight

Answer 32

temp is low so only exothermic rections can happen Barriers are hindered and no endothermic reactions no 3 body gas reactions as denisty is too low restricted to gas phase and surface chemistry

Answer 33

Collisions by molecules from ISM with surface

Answer 34

How often molecules stick to the surface dust, this depends on collision energy, nature of surface and grain size.

Answer 35

High temp. energy source is cosmic rays so lots of dust and photons being emitted. H3+ is main driver of chem

Answer 36

endothermic rxns impossible as temp is too low. No barrier. He+ is usually inert but it wants to be He so charge exchange

Answer 37

ISM pysical conditions and molecules available

Answer 38

Classical trajectories, newtons law of motion and cresu rennes

Answer 39

Silicate core, carbonaceous layer and then ices. Dust particles aggregates into crystalline structures and collect O from ISM to form silicates volatile molecules condense on surface of dust forming ices

Answer 40

Characteristic of composition large stars are likely to end in supernova and eject SiO3 into ISM. Heavy element burning starts also form carbon IR spec contains peaks from silicates and various C and O containning molecules. collisions with atoms that causes dust to emit IR

Answer 41

not spherical around 2 um transparent for many different wavelenghts and high energy photons do not break them high concentration of Si indicates they are formed from heavy stars.

Answer 42

Dust nay scatter light from distant stars out of the line of sight, reducing the amount detected and decreasing the luminosity of the star Id dust lines up in a magnetic field, and scatter light it changes the direction of the photon inducing polarization

Answer 43

Thermal and lateral moment

Answer 44

Height/ width of barrier and is largely time dependent and substrates - isotopes effect (D has higher probability than H)

Answer 45

Eley -rideal (chemiabsorption) | Langmuir - hinshelwood (physisorption)

Answer 46

Atoms adsorbs onto surface another atom passes by which interacts with particle on surface (head on head collision) strong interaction. Molecule formed which desorbs

Answer 47

two molecules/atoms adsorbs onto surface They diffuse across surface and interact when close together desorb once a molecule is formed

Answer 48

As atoms diffuse across surface it hard for them to build up so there are low abundances

Answer 49

Surface is not flat in reality, so can switch from chemisoportion and physisoprtion

Answer 50

The ability to convert external energy/matter into an internal process of self maintenance and production of its own components.

Answer 51

That the first self replicating system was a set of RNA molecules

Answer 52

1. short RNA oligonucleotides formed by a random event 2. Some oligonucleotides began to cataylse complimentary copies by acting as templates 3. chemical replication of dioligonucleotides led the evolution of self replicating RNA molecules.

Answer 53

1. 17 RNA ribozymes have been discovered that produces a large array of organic molecules 2. Formation of peptide bonds and the ability to build proteins may lead to a complex evolution favoured by proto - proteins 3. RNA is an intermediate in DNA synthesis which suggest it preceded DNA in evolutionary process

Answer 54

One molecule acts as a template and catalyses the reaction. molecules reversibly binds constituents A and B to form a termolecular complex This undergoes irreversible polymerisation and forms a duplex which dissociates to form two molecules.

Answer 55

1. Liquid over a large range of temps. 1 calory required to heat water by 1 degree. so if external temp changes drastically then internal temp wont 2. Ice is less dense that liquid water so frozen ice caps protect life below it 3. Water is polar, so has different solvation properites that discriminate between polar and non polar molecules which has led to formation of mixed phases such as membranes, microcompartmentalisation.

Answer 56

First prebiotic synthesis experiment that uses lightening strikes which produces many prebiotic building blocks eg amino acids The electrical discharge was struck in a primordial atmosphere and contained CH4, NH3, H2O and H

Answer 57

Stecker synthesis HCN polymerisation Formose reaction

Answer 58

Amino acids not formed in the electrical discharge but the condensed water reservoir. Formation of HCN and HCO. The carbonyl in HCO replaced by NH3. This reacts with HCN to form cyano amino compounds

Answer 59

HCN produced photocatalytically can polymerise in water when dissolved. Adenine is made this way and other purines can be made by intermediates in the polymerisation.

Answer 60

the formation of sugars from formaldehyde under alkaline catalyst. requires an inorganic catalysts, which may be present on prebiotic earth

Answer 61

Need inorganic phospate to make large RNA oligonucleotides and there is no way of activating phosphates groups. Phosphate can come from minerals in earth crusts and iron meteorites Chirality - need stereospecific molecules eg L amino acids. but how do you get stereoregular molecules from a racemic prbiotic soup. Polarised light - from dust particles scattering light that show dichroic scattering. Radiation would destroy one enantiomer over the other