Spectrophotometer PDF
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This document provides an overview of spectrometry, including electromagnetic radiation, different regions of the spectrum, and important laws in spectrophotometry. It covers topics such as wavelength, wave number, frequency, and the energy levels of molecules.
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Spectrometry- an analytical instrument used to observe the characteristic of a molecule through light. Electromagnetic radiation Complete system of energy propagated in wave form. Utilizes radiant energy (different forms of light, color and waves)-UV, Visible...
Spectrometry- an analytical instrument used to observe the characteristic of a molecule through light. Electromagnetic radiation Complete system of energy propagated in wave form. Utilizes radiant energy (different forms of light, color and waves)-UV, Visible and IR regions Wavelength- the length of the complete wave or wave cycle. Measures the distance between peaks (um or nm) Wave number- number of waves per cm Frequency- number of complete cycles Region Wavelength UV 200-380nm Visible 380-780nm Near IR 780-3000nm Medium IR 3-15um Far IR 15-300um 2 Theories of Radiant Energy Energy in the EM spectrum occurs in bundles called Photons or quanta Planck’s constant-describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T, when there is no net flow of matter or energy a. Theories of between the body and its environment; energy content possessed by a quantum of radiant energy Radiant Energy which determines whether a given chemical species absorbs or transmits radiant energy ABSORBANCE- light absorbed by the photons TRANSMISSION- light transmitted from the sample Energy in the EM spectrum propagated in wave form A molecule exist only in certain permitted states and cannot possess any arbitrary amount of energy Initial to higher energy state (absorbance of energy to photons) All molecules in nature contain a specific quantity of energy at a given temperature (Internal energy, E); sum of Electronic energy (Ee), vibrational Energy (Ev) Rotational Energy (Er) and Translational Energy (Et) E=Ee+Ev+Er+Et Translational Energy is not used in Spectrometry Ee-UV-Vis region Et and Ev-IR region UV (185 to 380nm) Vis (380-780nm) Molecules are activated only in this spectrum Ee and works on: Non-bonding electrons/n electrons: O, S, N or X Sigma UV and Visible Pi Spectroscopy Radiant energy---molecules (ground to a higher state) The higher state is called the antibonding orbitals where when sigma and pi reached it they become sigma star and pi star respectively Sigma electrons- tightly bond with carbon atoms and the energy required to disrupt the bond is in FAR UV (
