Electromagnetic radiation is a self-propagating wave with an electric component and a magnetic component. These 2 components oscillate at right angles to each other and are in phase with each other.Electromagnetic radiation is a self-propagating wave with an electric component and a magnetic component. These 2 components oscillate at right angles to each other and are in phase with each other. Electromagnetic radiation travels at the speed of light. In fact, the “light” in this room is electromagnetic radiation.Electromagnetic radiation travels at the speed of light. In fact, the “light” in this room is electromagnetic radiation. CH 104: INFRARED ANALYSIS OF AN UNKNOWN ORGANIC COMPOUND THE ELECTROMAGNETIC SPECTRUM

decrease increase The wavelength (λ, the length of 1 cycle in meters) times the frequency (ν, the number of cycles per second) equals the speed of light (c, a constant that equals 3.0 x 10 8 meters/second). That is,The wavelength (λ, the length of 1 cycle in meters) times the frequency (ν, the number of cycles per second) equals the speed of light (c, a constant that equals 3.0 x 10 8 meters/second). That is, c = λν = 3.0 x 10 8 meters/second If λ increases, then ν must so that c remains constant.If λ increases, then ν must so that c remains constant. If λ decreases, then ν must so that c remains constant.If λ decreases, then ν must so that c remains constant. THE ELECTROMAGNETIC SPECTRUM

Electromagnetic radiation is also a stream of energy packets called photons.Electromagnetic radiation is also a stream of energy packets called photons. The energy of a single photon (E, in joules) equals Planck’s constant (h, x joule second) times the frequency (ν, the number of cycles per second). That is,The energy of a single photon (E, in joules) equals Planck’s constant (h, x joule second) times the frequency (ν, the number of cycles per second). That is, E = hν = hc/λ If the frequency (ν) increases, the energy (E).If the frequency (ν) increases, the energy (E). If the wavelength (λ) decreases, the energy (E).If the wavelength (λ) decreases, the energy (E). THE ELECTROMAGNETIC SPECTRUM increases increases

The ultraviolet (UV) region of the electromagnetic spectrum includes all wavelengths from 10 nanometers (nm) to 380 nm. The vacuum-ultraviolet region goes from 10 nm to 200 nm because air absorbs strongly at these wavelengths so instruments must be operated under a vacuum in this region. The near-ultraviolet region goes from 200 nm to 380 nm.The ultraviolet (UV) region of the electromagnetic spectrum includes all wavelengths from 10 nanometers (nm) to 380 nm. The vacuum-ultraviolet region goes from 10 nm to 200 nm because air absorbs strongly at these wavelengths so instruments must be operated under a vacuum in this region. The near-ultraviolet region goes from 200 nm to 380 nm. The visible (Vis) region goes from 380 nm to 780 nm and can be seen by the human eye.The visible (Vis) region goes from 380 nm to 780 nm and can be seen by the human eye. The infrared (IR) region goes from 0.78 micrometers (μm) or 780 nm to 300 μm. However, the near-infrared (0.8 μm to 2.5 μm) and the NaCl-infrared regions (2.5 μm to 16 μm) are the most commonly used by analytical chemists.The infrared (IR) region goes from 0.78 micrometers (μm) or 780 nm to 300 μm. However, the near-infrared (0.8 μm to 2.5 μm) and the NaCl-infrared regions (2.5 μm to 16 μm) are the most commonly used by analytical chemists. THE ELECTROMAGNETIC SPECTRUM

Humans see color when an object transmits or reflects visible light.Humans see color when an object transmits or reflects visible light. More specifically, an object may absorb specific wavelengths of electromagnetic radiation. The unabsorbed wavelengths from the visible region are transmitted and seen as color.More specifically, an object may absorb specific wavelengths of electromagnetic radiation. The unabsorbed wavelengths from the visible region are transmitted and seen as color. For example, leaves are green because the pigment chlorophyll absorbs violet, blue, and red light.For example, leaves are green because the pigment chlorophyll absorbs violet, blue, and red light. Why are violets violet?Why are violets violet? Violets are violet because they absorb green.Violets are violet because they absorb green. THE ABSORPTION OF ELECTROMAGNETIC RADIATION BY MOLECULES

There are 3 ways that a molecule can absorb electromagnetic radiation. All 3 ways raise the molecule to a higher internal energy level. All these changes in energy are quantized; that is, they occur at discrete levels.There are 3 ways that a molecule can absorb electromagnetic radiation. All 3 ways raise the molecule to a higher internal energy level. All these changes in energy are quantized; that is, they occur at discrete levels. Rotational Transitions: The molecule rotates around various axes. Rotational transitions require the least amount of energy. Purely rotational transitions can occur in the far-infrared and microwave regions.Rotational Transitions: The molecule rotates around various axes. Rotational transitions require the least amount of energy. Purely rotational transitions can occur in the far-infrared and microwave regions. Vibrational Transitions: Atoms or groups of atoms within a molecule vibrate relative to each other. Vibrational transitions require an intermediate amount of energy and typically begin to occur in the mid- infrared and far-infrared regions. Therefore, as energy is increased (or wavelength is decreased) vibrational transitions occur in addition to rotational transitions.Vibrational Transitions: Atoms or groups of atoms within a molecule vibrate relative to each other. Vibrational transitions require an intermediate amount of energy and typically begin to occur in the mid- infrared and far-infrared regions. Therefore, as energy is increased (or wavelength is decreased) vibrational transitions occur in addition to rotational transitions. Electronic Transitions: An electron within a molecule is typically promoted from its ground state to an excited state. Electronic transitions require the most amount of energy and typically begin to occur in the visible and ultraviolet regions. Therefore, as energy is increased (or wavelength is decreased) electronic transitions occur in addition to vibrational and rotational transitions.Electronic Transitions: An electron within a molecule is typically promoted from its ground state to an excited state. Electronic transitions require the most amount of energy and typically begin to occur in the visible and ultraviolet regions. Therefore, as energy is increased (or wavelength is decreased) electronic transitions occur in addition to vibrational and rotational transitions. THE ABSORPTION OF ELECTROMAGNETIC RADIATION BY MOLECULES

A company that sells stearyl alcohol (C 18 H 37 OH) to the rubber industry received a complaint from 1 of its customers that its product was off color. The customer returned a sample of this off-color alcohol. This sample was used to identify the contaminant or contaminants that were causing this problem.A company that sells stearyl alcohol (C 18 H 37 OH) to the rubber industry received a complaint from 1 of its customers that its product was off color. The customer returned a sample of this off-color alcohol. This sample was used to identify the contaminant or contaminants that were causing this problem. The contaminants were separated by chromatography. The separated contaminants were identified by infrared (IR) spectroscopy.The contaminants were separated by chromatography. The separated contaminants were identified by infrared (IR) spectroscopy. CASE STUDY: IR SPECTROSCOPY AND AN OFF-COLOR ALCOHOL

In review, IR spectroscopy measures the absorption of electromagnetic radiation caused by the vibration of atoms or groups of atoms within a molecule. Different molecules will have different IR spectra.In review, IR spectroscopy measures the absorption of electromagnetic radiation caused by the vibration of atoms or groups of atoms within a molecule. Different molecules will have different IR spectra. CASE STUDY: IR SPECTROSCOPY AND AN OFF-COLOR ALCOHOL

IR spectroscopy suggested the off-color was in part caused by long oil soya alkyd, a common ingredient in paint.IR spectroscopy suggested the off-color was in part caused by long oil soya alkyd, a common ingredient in paint. The customer was contacted and confirmed that painters worked in his plant after the alcohol was received and before the off-color was noticed. The off-color was caused by chemicals that evaporated from the paint and were absorbed by the alcohol.The customer was contacted and confirmed that painters worked in his plant after the alcohol was received and before the off-color was noticed. The off-color was caused by chemicals that evaporated from the paint and were absorbed by the alcohol. CASE STUDY: IR SPECTROSCOPY AND AN OFF-COLOR ALCOHOL

SOURCES Christian, G.D Analytical Chemistry, 3rd ed. New York, NY: John Wiley & Sons, Inc.Christian, G.D Analytical Chemistry, 3rd ed. New York, NY: John Wiley & Sons, Inc. Harris, D.C Quantitative Chemical Analysis, 5th ed. New York, NY: W.H. Freeman Company.Harris, D.C Quantitative Chemical Analysis, 5th ed. New York, NY: W.H. Freeman Company. Raven, P.H., R.F. Evert, H. Curtis Biology of Plants, 3rd ed. New York, NY: Worth Publishers, Inc.Raven, P.H., R.F. Evert, H. Curtis Biology of Plants, 3rd ed. New York, NY: Worth Publishers, Inc. Spencer, J.N., G.M. Bodner, L.H. Rickard Chemistry Structure and Dynamics, 3rd ed. New York, NY: John Wiley & Sons, Inc.Spencer, J.N., G.M. Bodner, L.H. Rickard Chemistry Structure and Dynamics, 3rd ed. New York, NY: John Wiley & Sons, Inc. Wikipedia Image:Light-wave.png. Available: [accessed 2 September 2006].Wikipedia Image:Light-wave.png. Available: [accessed 2 September 2006].