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Meijer Astrochem Flashcards

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1
Q

Why in space are collisions so few and far in-between?

A

Low densities and temp

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2
Q

How does the chemistry of space differ if close to sun or star or in the presence of interstellar radiation?

A

Near the sun and strata temp is high which may drive certain chemical reactions

Radiation could degrade molecules

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3
Q

True or false - the detection of Molecules in space is due to the stability of the molecules

A

False - the presence of other molecules may be due to the fact that they are precursors

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4
Q

What are the three elements of the Big Bang

A

Big Bang nucleosynthesis
Cosmic microwave background radiation
Inflation/expanding universe

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5
Q

What happens in the first 100 seconds of the Big Bang

A

All elementary forces equal. Universe is the length of plank. As time goes on, temp decreases and elementary forces separate. Quarks present and then protons and neutron interconvert and eventually protons dominate. At end of 100s neutron and protons combine to form deuterium.

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6
Q

Why does Big Bang nucleosynthesis stop

A

Temp too low and density is too low

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7
Q

Why is there cosmic background radiation

A

Temp is now low enough that there is decoupling
Electrons and nuclei combine to form neutral atoms.

Photons and matter decouple and no longer interact. Universe becomes transparent and photons fly uninterrupted through universe - cosmic background radiation

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8
Q

What distribution does cosmic background radiation give?

A

At decoupling Matter and radiation are in thermal equilibrium. Photon energy distribution gives a black body curve with a temp of 2.725

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9
Q

What does the BB distribution curve Suggest

A

If there was massive star formation it would perturb the curve. universe was initially hot but has been cooling down ever since

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10
Q

what is the doppler effect?

A

When electromagnetic waves moves towards the observer the transition shifted to smaller wavelengths - blue shifted
When electromagnetic waves move away from the observer, the transition is shifted to longer wavelengths - red shifted

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11
Q

how does the doppler effect support the big bang?

A

when the universe expands CMBR is detected at longer wavelenghts

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12
Q

what is the definition of black body radiation?

A

an object that emits and absorbs all wavelengths of radiation at equal efficiency

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13
Q

what are the other properties of black body radiation?

A

At T> 0 K, emits radiation at all wavelengths
As temperature increases object emits more light at all wavelengths
As temperature increases it emits more radiation at shorter wavelenghts
have a wavelength distribution

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14
Q

what is the stefan boltzman law

A

Relates the amount of energy emitted from a blackbody object to its temperaturea

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15
Q

what are the equations to calculate the parralax?

A 
d = 1/ Theta
Theta = Distance ? 1 parsec (3.26 ly or 3.08x10^16 m )
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16
Q

how is hubbles law related to the age of the universe?

A

V = H + d

t = d/V sub in first equation you get t = 1/V

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17
Q

How does the abundance and distribution of elements in space prove the big bang?

A

Most abundant is He and H - makes up most of the universe. It is all primordial.
Light elements made in big bang nucleosynthesis

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18
Q

what is the light source and the detector in astronomy?

A

The star is the light source and the telescope is the detector

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19
Q

what is the modified beer lambert law for spectroscopy for space?

A

I = Io e - (aplha * l )

alpha is the absorption peer parsec

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20
Q

what are the 5 different ways that matter interacts with photons?

A

Elastic and inelastic scattering
Spontaneous emission and adsorption
Stimulated emission

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21
Q

What is elastic scattering (rayleigh)

A

Atom interacts with photon and energy of photon is not changed

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22
Q

what is Inelastic scattering (raman)

A

Atom absorbs photon and photon is remitted at a different wavelength. Atom either absorbs photon energy or gives photon additional energy

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23
Q

What is stimulated emission?

A

atom is inn excited state and when a photon of right energy/wavelength passes. excited returns to ground state and emits photon of exact energy as incoming photon

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24
Q

are photons wisth shorter wavelenghts scattered more or less than photons with longer wavelengths?

A

They are scattered more

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25
Q

what are the problems associated with spectroscopy in space?

A

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

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26
Q

what is lifetime broadening?

A

The transitions are naturally broadened by the lifetime of excited state

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27
Q

what is pressure broadening?

A

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

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28
Q

why is pressure broadening not so much of a problem?

A

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

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29
Q

what bring the onset of line broadening

A

Doppler effect

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30
Q

what are the laws of gravity?

A

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

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31
Q

what is the criteria for star formation?

A

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

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32
Q

outline the process of star formation?

A
  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
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33
Q

what is the requirement for spontaneous collapse of the star

A

Mass of star achieves a critical mass (jeans mass)

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34
Q

what is the proton proton cycle

A
  1. Fusion of two protons
  2. Proton capture
  3. He fusion
    source of energy for young stars
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35
Q

what is the triple alpha process

A

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

36
Q

what is the CNO cycle?

A

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

37
Q

describe waht low mass stars are?

A

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

38
Q

what are high mass stars?

A 
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
39
Q

What is a neutron star

A

Density matter of cloud collapses and core consist of neutrons

40
Q

What is the supernova?

A

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

41
Q

what type of elements are formed in the supernova

A

Heavy elements

42
Q

What is MASER

A

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

43
Q

why is it difficult to detect hydrogen?

A

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

44
Q

What is the key feature in the detection of hydrogen?

A

21 cm line

45
Q

How does the 21 cm line arise?

A

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

46
Q

what are diffuse interstellar bands (DIB)?

A

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

47
Q

what does the DIB suggest?

A

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

48
Q

What does mapping CO give?

A

Density plot, indicates where there is most interaction with ISM

49
Q

To form a star you need to remove heat as pressure builds up, a cooling agent is needed. What is it?

A

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

50
Q

what are some of the issues in detecting molecules in space?

A

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.

51
Q

what are OH masers?

A

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.

52
Q

what is the ISM

A

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

53
Q

what are the most abundant molecules in the ISM

A

H,C,N,O so dominate molecular formation

54
Q

what are the regions of the ISM

A

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

55
Q

why do clouds viewed through a dust cloud have short wavelength radiation missing from their spectra?

A

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

56
Q

what are the limits on RXN is the ISM

A

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

57
Q

how is dust surface chemistry initiated?

A

Collisions by molecules from ISM with surface

58
Q

what is the sticking probability?

A

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

59
Q

True or false: Adsorption onto a surface can result in dissociation producing reactive species available for chem reactions

A

True

60
Q

describe the circumstellar disk?

A

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

61
Q

describe the chemistry in Dark clouds

A

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

62
Q

what does the rate of reaction depend on?

A

ISM pysical conditions and molecules available

63
Q

how are rate constants obtained?

A

Classical trajectories, newtons law of motion and cresu rennes

64
Q

describe the composition of interstellar dust particles

A

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

65
Q

describe the IR spec of interstellar dust particles.

A

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

66
Q

what are the characteristics of IS dust?

A

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.

67
Q

how does Interstellar dust give visual extinction and polarisation of light?

A

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

68
Q

what does the sticking probability depend on?

A

Thermal and lateral moment

69
Q

what does tunneling depend on

A

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

70
Q

what are the two mechanisms for sticking reactions

A

Eley -rideal (chemiabsorption)

Langmuir - hinshelwood (physisorption)

71
Q

Describe the Eley -rideal mechanism?

A

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

72
Q

Describe the langmuir - hinshelwood mechanism?

A

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

73
Q

What the issues with the Langmuir mechanism

A

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

74
Q

what are both the mechanism idealised?

A

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

75
Q

what is the definition of life?

A

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

76
Q

what does the RNA hypothesis suppose?

A

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

77
Q

what scenario does the catalytic and transferring properties of RNA propose.

A
  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.
78
Q

What evidence is there to support the RNA theory

A
  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
79
Q

what is the three stop model for ribozyme catalysis

A

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.

80
Q

what are the properties of water that make it the solvent for life?

A
  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.
81
Q

describe the ulrey miller experiments?

A

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

82
Q

what are the three prebiotic chemistry reactions

A

Stecker synthesis
HCN polymerisation
Formose reaction

83
Q

what is the stecker synthesis?

A

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

84
Q

what is HCN polymerisation

A

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.

85
Q

what is the formose reaction

A

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

86
Q

what are the problems with forming molecules needed for life in space?

A

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

Chemistry (22 decks)

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