Astrochemistry--Exam 1

Astrochemistry

The study of formation and destruction of molecules in the Universe, their interaction with radiation, and their feedback on the physics of the environment

Combination of physics, chemistry, astronomy, and biology

Roles of Atoms

• nuclear fusion for the creation of stars

• were the first components formed in the universe, leading to the development of molecules and complex structures.

Roles of Molecules

• creation of complex molecules (H2, CO) that led to severe cooling, stimulating the creation of stars, allowing for more complex molecules to be created

• Became the building block for habitable environments

Components of Interstellar Matter

• gas (H2, CO)

• dust (used are the holding ground for chemical reactions to occur due to the accumulation of particles)

Importance of Molecular Bonding

• basis for the creation of life

  ex. CO———→ more complex organic molecules

  H20———→ basis for life

Big Bang Theory

The universe is expanding from an initial hot, dense state at a finite time in the past

Cold Dark Matter Model

the energy density of the universe today is almost entirely contributed by a cosmological constant and by matter (mostly CDM)

Black Body Characteristics

• absorbs and emits radiation at all wavelengths with equal efficiency

• produces a continuous electromagnetic spectrum across all wavelengths

Cosmic Microwave Background Radiation

• fossil radiation form the Big Band (follows BBS)

• it is isotropic (appearing equally intense in all directions like the BBS states)

• COBE satellite measured the CMBR and confirmed its uniformity across the sky, providing evidence for the Big Bang Theory

• Doppler effects from the Milky Way/Local Group’s motion must be accounted for in measurements of CMBR

Stellar Classification

• measure temperature using B/C ratio (ratio of intensities in different spectrum bands)

• photosphere (surface temperature) is used to determine the star’s color

• Star’s color and temp tells us what the star is made of and what stage in life it is

Parallax

• How astronomers measure distance between stars

• Measures apparent motion of nearby stars against distant stars as Earth orbits the Sun

Constellation

Historically named star patterns

Galaxies

• objects in the sky that are not stars or plants in the solar system

• Shapes: elliptical, spiral, and irregular

Galaxies and Clusters

Stars form galaxies through gravitational agglomeration, and galaxies themselves form into clusters, illustrating that matter in space is clumped rather than uniformly spread.

Dark Ages

• a phase of the universe that occured after the Big Bang but before the first stars were formed

Formation of the First Stars

• happened 400 million years after BB

• occured when atoms/gas collapsed together and the formation of H2 cooled the universe

• Stars then started to produce C,N,O which are vital for organic molecule formation

Expanding Universe

• proposed by Alexander Friedman

• observation data confirmed the universe’s expansion

• used linked molecular processes with cosmic phenomena to explain the universe’s structure and history

• confirmed because of red shift

Red Shift

• a dimensionless measure of the fractional change in wavelength due to cosmic expansion

• proportional to a galaxy’s distance, which corresponds to the time light traveled from the galaxy

Hubble’s Law

• describes the relationship between a galaxy’s redshift and its distance

• Hubble constant determines the rate of expansion

Importance of Molecules

Spectral lines tell us:

• gas temp and density

• ionization state and movement of gas clouds

Molecular composition can tell us:

• astrochemical processes

• possible prebiotic chemistry

• age of interstellar clouds/protoplanetary discs

Trible-Alpha Process (H-alpha emission)

At extreme temp and pressure, three helium nuclei (alpha particles) fuse to form a carbon

H3+

• key intermediate for ion-neutral reactions

• synthesis for water and complex organic molecules

CO

• abundant in the cold, dense regions of molecular clouds where ice forms on dust grains

• forms complex organic molecules

Absorption vs emission spectra

Absorption: energy that got absorbed is black that that wavelength

Emission: energy that got absorbed is and deflected at a different angle is only picked up, everything else is black

Infrared Spectroscopy

• sees atoms vibrate with frequencies in IR range

• determines chemical groups and provides conductivity analysis

• for matching bands, go to a database

FTIR

Uses beam shot through a crystal and bouncing back and forth with IR to measure sample vibrations and give us peaks

Energy Dispersive X-Ray Spectroscopy

• microanalysis; Z>3 but sometimes 2; 0.1-0.5 wt%

• bremsstrahlung x-ray (atomic number)

• characteristic x-ray (energy peaks)

  Components:

  • Detector (only allows x-rays and uses energy trapped in silicon to create a current with a dielectric)

  • Pulse Processor (coverts voltage pulse to energy levels and filters noise)

  • MCA (processes data and displays)