Astrochemistry and Cosmochemistry

Astrochemistry and Cosmochemistry

• Astrochemistry: study of abundance and reactions of molecules in the Universe and their interaction with radiation
• Cosmochemistry: study of abundance of elements, isotope ratios in the Solar System (meteorites)
• Molecular Astrophysics: study of interstellar atoms, molecules, and interaction with radiation
• Solar Spectra: study of spectral nature of light, led to the development of the first spectroscope

Spectroscopy

• Study of light from an object and its interaction with matter
• Experimental Spectroscopy: detection of molecules within solar systems and interstellar medium
• Spectrometer: instrument used to observe spectral lines present within solar radiation
• Key contributors to spectroscopy:
  • William Hyde Wollaston: built a spectrometer
  • Joseph Von Fraunhofer: quantified spectral lines
  • Charles Wheatstone: discovered emission spectra of different metals
  • Leon Foucault: demonstrated identical absorption and emission lines from same material at different temperatures
  • Johann Balmer: discovered Balmer Series of spectral lines in hydrogen
  • Johannes Rydberg: developed Rydberg Formula to describe spectral lines in hydrogen

Atomic Models

• Ernest Rutherford's Model: dense nucleus surrounded by a cloud of electrons
• Bohr's Model: electrons in discrete orbits around the nucleus, similar to planetary orbits
• Ground State: electron in its default orbit
• Excited State: electron must absorb energy to transition to a higher energy level
• Wave Model: atom as a sinusoidal wave with an oscillating electric field and perpendicular magnetic field
• Amplitude (A): height of wave's electric vector
• Wavelength (λ): distance between peaks of the wave

Electromagnetic Spectrum

• Range of all types of electromagnetic radiation, characterized by wavelength or frequency
• Different energies allow monitoring of different types of interactions with matter
• Visible Light (350-780 nm): radiation that can penetrate Earth's atmosphere and be detected on the surface

Spectra

• Range of electromagnetic energy separated by wavelength
• Types of Spectra:
  • Continuous Spectrum: thermal or blackbody spectrum, energy of all wavelengths
  • Discrete Spectrum: energy at a particular wavelength, emission (bright lines) and absorption (dark lines)

Doppler Effect

• Change in frequency of a wave related to an observer moving relative to the wave source
• Christian Doppler (1842)
• Blue light has a higher frequency than red light

Hubble's Law

• Hubble Constant: 70 km/s/Mpc
• Age of the Universe: approximately 13.8 billion years as of 2015

Atoms and Molecules

• Atom: smallest constituent unit of a chemical element
• Molecule: group of two or more atoms held together by chemical bonds
• Compound: substance formed when two or more elements mix chemically

Emission Nebulae and Ionized Hydrogen

• Emission Nebulae: visible when electrons recombine with ionized hydrogen, emitting visible light
• Ionized Hydrogen (H II) regions: visible near red hot stars, UV ionizes hydrogen
• Neutral Hydrogen Clouds: do not emit visible light, but can be seen when light from a star passes through the cloud
• 21-cm Radiation: neutral hydrogen emits a photon when electron spontaneously flips

Interstellar Gas and Dust

• Ultra-hot Interstellar Gas: temperature of millions of degrees, formed from supernova explosion
• Molecular Clouds: dense regions where complex molecules can be formed
• Interstellar Dust: made of various substances, blocks and scatters light, and emits infrared light
• Dark Nebulae: when light from other stars is blocked by dust, creating dark areas
• Extinction: light scattered off dust particles, preventing it from reaching us

IR Spectroscopy

• Carboxylic Acid (O-H): strong, broad peak around 3000-2500 cm^-1
• Alcohols (O-H): strong, broad peak around 3650-3200 cm^-1
• Aldehydes (C-H): two peaks, one around 2900 cm^-1 and another around 2700 cm^-1
• Ketones (C=O): strong peak around 1750-1705 cm^-1
• Esters (C=O): strong peak around 1750-1735 cm^-1

Spectroscopy and Atomic Models

• A spectrograph is a device that separates light into its component colors, producing a spectrum.
• Types of spectra:
  • Continuous spectrum: energy of all wavelengths, emitted by stars, planets, and moons, depends on temperature
  • Discrete spectrum: energy at a particular wavelength, produced by emission and absorption of energy by materials
• Doppler Effect: change in frequency of a wave in relation to an observer who is moving relative to the wave source
• Hubble's Law: Hubble Constant = 70 km/s/Mpc, Age of the Universe = 13.8 billion years

Astrochemistry and Cosmochemistry

• Astrochemistry: study of abundance and reactions of molecules in the Universe and their interaction with radiation
• Cosmochemistry: study of abundance of elements, isotope ratios in the Solar System
• Molecular Astrophysics: study of interstellar atoms, molecules, and interaction with radiation
• Solar Spectra: spectral nature of light, first spectroscope, and experimental spectroscopy

Atomic Models

• Ernest Rutherford's Model: dense nucleus surrounded by a cloud of electrons
• Bohr's Model: electrons surrounding the nucleus exist in discrete orbits, like planets orbiting the Sun
• Wave Model: an atom is a sinusoidal wave traveling in space with an oscillating electric field and perpendicular magnetic field

Electromagnetic Spectrum

• Range of all types of electromagnetic radiation, characterized by wavelength or frequency
• Types of radiation:
  • Visible light (350-780 nm): radiation that can penetrate our atmosphere and be detected on the Earth's surface
  • Photon: tiniest particle of light at a certain wavelength, requires release of same energy to become excited

Spectrometers in Spacecraft

• Mars Exploration Rover: Mini-TES (Miniature Thermal Emission Spectrometer), MB (Mossbauer Spectrometer), APXS (Alpha Particle X-ray Spectrometer)
• Cassini-Huygens: VIMS (Visual and Infrared Mapping Structure) for data on surface, rings, and atmosphere of Titan and Saturn

IR Spectroscopy Graphs

• Carboxylic Acid (O-H): strong, broad peak around 3000-2500 cm^-1, requires C=O in zone 4
• Alcohols (O-H): strong, broad, elongated "U" shape around 3650-3200 cm^-1
• Aldehydes (C-H): two peaks around 2900 cm^-1 and 2700 cm^-1, medium length
• Ketones (C=O): strong peak around 1750-1705 cm^-1, looks for signs of conjugation
• Esters (C=O): strong peak around 1750-1735 cm^-1, looks for signs of conjugation

Molecular Clouds and Interstellar Gas

• Emission Nebulae: visible light emitted when electrons recombine with ionized hydrogen
• Ionized Hydrogen (H II) regions: visible near red hot stars, UV ionizes hydrogen
• Neutral Hydrogen Clouds: do not emit visible light, can be seen when light from a star passes through the cloud
• 21-cm Radiation: neutral hydrogen can be collisionally excited, emitting 21-cm photons
• Ultra-hot Interstellar Gas: temperature of millions of degrees, materials from supernova explosion
• Molecular Clouds: dense regions where complex molecules can be formed, such as ammonia, benzene, acetylene
• Interstellar Dust: made of different substances, blocks and scatters light, reflects light from nearby stars, cooler temperatures emit infrared light

Timeline of the Early Universe

• Big Bang Theory: originally conceptualized by German Priest George Lemaitre
• 3-20 minutes (Nucleosynthesis): temperature drops, atomic nuclei formed, Hydrogen, Helium, and Lithium formed
• 3 minutes - 240,000 years (Photon Epoch): soup of atomic nuclei, photons could not travel far
• 240,000 - 380,000 years (Recombination and Decoupling): recombination forms neutral atoms, space becomes "transparent", Cosmic Microwave Background radiation relic
• 300-500 million years (Star formation): first generation stars born, massive, hot, luminous, ultraviolet blue