9_IR_spectroscopy_answers

9_IR_spectroscopy_answers - Spectroscopy Infrared and...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Spectroscopy Infrared and Nuclear Magnetic Resonance Electric Field Magnetic Field ± w a v e l n g th Electric wave Magnetic wave Direction of motion of the light beam Light is an electromagnetic phenomenon. A beam of light consists of two mutually perpendicular oscillating fields: an oscillating electric field and an oscillating magnetic field λ
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Equations νλ = c λ ν c = c = frequency ( ν ) number of cycles per second (units: cycles s -1 = Hertz, Hz) wavelength ( λ ) distance spanned by one cycle (units: meters, m) Wavenumber number of cycles in 1 cm or inverse of the wavelength in cm (units: cm -1 ) speed of light ( c ) 2.99892458 x 10 8 m s -1 in a vacuum Planck’s constant ( h ) = 6.626076 x 10 -34 Joules s Larger the frequency smaller the wavelength Larger the frequency larger the wavenumber 1 = wavenumber The fundamental mechanism responsible for this radiation is the acceleration of a charged particle. Whenever a charged particle undergoes acceleration, it must radiate energy at the speed of light as packets of energy called photons. The energy of a photon is inversely proportional to the wavelength hc E = or Smaller the wavelength or larger the frequency the larger the energy of the photon lower energy, smaller frequency, larger wavelength, smaller wavenumber higher energy, greater frequency, smaller wavelength, larger wavenumber h E =
Background image of page 2
3 Spectroscopy What is it? Spectroscopy detects transitions between the quantized energy levels of an atom or molecule, where the energies are due to some internal motion of the atom or molecule. In atoms, these motions are due to the changes in the electronic configuration . In molecules these internal motions arise from changes in either rotations (microwave spectroscopy) vibrations (infrared spectroscopy), electronic excitations (uv-visible and photoelectron spectroscopy) or nuclear spin orientation (nuclear magnetic resonance). How do we do it? Transitions are observable by measuring discrete frequencies of electromagnetic radiation that are absorbed or emitted by atoms or molecules. Why do we do it? By characterizing the energy levels of a molecule, we can describe the geometry of that molecule, including the lengths and strengths of its bonds, the identity and positions of its constituent atoms, the energies of its molecular orbitals, and the overall framework and shape of the molecule. (Chem 129 notes by Dr. B. Power. 1997)
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 Regions of the electromagnetic spectrum and the types of molecular motions 100 cm (cm-1) 108 1 cm 10 -2 10 -1 10 -3 10 -3 104 106 11 0 0 100 m ± 1 m ± 10 nm wavenumber 10 m 100 pm wavelength 3 x 10 6 3 x 10 8 3 x 10 10 3 x 10 12 3 x 10 12 3 x 10 14 3 x 10 18 10 10 3 10 5 10 7 10 9 frequency (Hz) energy (J/mol) low energy high energy STD broad cast TV microwaves IR Visible UV x-rays
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 33

9_IR_spectroscopy_answers - Spectroscopy Infrared and...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online