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CHEMICAL SPECTROSCOPY
by
R. E.~DD Lecturer in Chemistry,
King's College,
University of Durham,
Newcastle-upon-Tyne (England)
ELSEVIER PUBLISHING COMPANY AMSTERDAM - NEW YORK
1962
•
CONTENTS
Introduction . . . . . .
CHAPTER l. EXPERIMENTAL METHODS OF SPECTROSCOPY
Wavelength and Frequency . Wave number, 6
Energy and Frequency . . . General Experimental Arrangement Sources ............ .
Diseharge tubes, 13 - Ares and sparks, 15 - Ineandeseent sourees, 15 -Continuum diseharge sourees, 17 - Monochromatic high frequency sources, 18
Spectrographs and Monochromators Prisms and prism materials . Gratings Filters ...... . Detectors ..... .
Photographie detection, 31 - Photocells, 32 - Thermal deteetors, 34 -Mierowave deteetors, 35
Presentation . . . . . Photographs, 36 - Direct recording, 37 - Comparative recording, 38 -Standard presentation, 39
Resolution. . . . . . . . . . . . . . . . . . . . . . Wavelength or Frequency Calibration ........ .
Optical spectrometers, 42 - Microwave and radio frequencies, 45 Intensity Measurement . . . . . . . . . . . . : . . .
Beer's law, 47 - Additivity of optical density, 49 - Integrated intensity, 50 - Raman scattering intensity, 51 - Microwave absorption intensity, 52
Sample Treatment . . . . . . . . . . . . . . . . . . . . . Absorption eells, 53 - Measurement and adjustment of path length, 54 -Solvent eompensation, 55 - Other factors, 55 - Solvents, 56 - Solids, 58 -Temperature variation, 58 - Quantities required, 59 - Mierowave absorption, 59
Raman Spectra Polarization, 62
Fluorescence . References . . .
l
3
4
7 8
12
19 23 27 29 31
39 42
47
53
60
viii CONTENTS
CHAPTER 2. CHARACTERIZATION OF STATES: ELECTRONIC STATES
Quantum Mechanical Basis .............. . Fundamentalpostulates, 72 - Characteristic states, 73 - Degeneracy, 74 -Uncertainty principle, 74
General Interpretation of Spectra . . . . . . . . . . . . . . Separation of motion in molecules, 76 - Band spectra, 78 - Fluorescence and Raman spectra, 79 - Effect of magnetic and electric fields, 80 - Population of levels, 81
Spectral Activity: Selection Rules . . . . . . . Electronic states of Hydrogen and Alkali Metals
Hydrogen atom, 84 - Alkali metals, 88
Angular Momentum . . . . . . . . . . . . . . . . . . . . Space quantization, 92 - Relativistic treatment, 93 - Multiplet spectra, 96 - Electron spin and the Vector model, 96 - Space quantization of J , loo - Zeeman effect, 101
Spin Resonance . . . Paramagnetic resonance, 103 - Nuclear spin resonance, 104
Helium .... . ........ . ...... . Singlet and triplet levels, 108 - Symmetry of observed states, l 10 - Energy and electron correlation, l l l
67
71
75
92
103
107
Pauli's Principle . . . . . . . . . . . . . . . . . . . . . . II2 The periodic table, u3 - Deducing configuration from spectral terms, u6
Electronic ~tates in Molecules . . . . . . . . . . . . . . . . rr8 Molecular orbitals, u8 - The hydrogen molecule-ion, H 2+, 122 - Hydrogen molecule, 122 - Multiplicity of molecular states, 125
References. . . . . . . . . . . . . . . . . . . . . . . . . 127
CHAPTER 3. CHARACTERIZATION OF STATES: NUCLEAR MOTION 129
Vibrational States of Diatomic Molecules . . . . . . . . 129 Harmonie diatomic oscillator, 131 - Vibrational spectrum, 133 - Raman spectrum, 136 - Anharmonic oscillator, 137 - Vibration in electronic transitions, 139 - Analysis of a band system, 141 - Sequences, 144 - Poten-tial energy curves, 147 - Force constants in diatomic molecules, 150
Dissociation Energy . . . . . . . . . . . . . . . . . . . . 151'
Vibrational States of Polyatomic Molecules. . . . . . . . . . 157· Normal coordinates, 159 - Quantum mechanical description, 163 - Sym-metry of the mechanical model, 164 - Symmetry of vibrational states, 168 -Selection rules for infra-red spectra, l 70 - Selection rules for Raman spectra, r72 - Centrosymmetric molecules, 173 - Polarization of Raman lines, 174 -Use of character tables, 175 - Determination of molecular symmetry, 177 -Limitations, 181 - Assignment of frequencies, 182 - Force constants, 184
Rotational States . . . . . . . . . . . . . . . . . . . . . 185 Linear and diatomic molecules, 186 - Spherical top molecules, 193 - Symmetrie top molecules, 193 - Asymmetrie top molecules, 196 - Stark effect, 197 - Centrifugal stretching, 200 - Interaction between vibration and
CONTENTS
rotation, 200 - Rovibrational transitions, 201 - Unresolved bands, 206 -Molecular dimensions from rotational structures, 207 - Rotation in electronic states, 210
ix
Nuclear spin. . . . . . . . . . . . . . . . . . . . . . . . 2n Symmetry properties including nuclear spin, 212 - Interaction with rotation, 213
References. . . . . . . . . . . . . . . . . . . . . . . . . 216
CHAPTER 4. lNTERACTIONS AND EMPIRICAL CORRELATIONS
Chromophores, 218
Ultraviolet and Visible Absorption Spectra . . . . . . Single bonds and saturated molecules, 219 - Non·bonding electrons, 221 -N -+ R transitions, 221 - Double bonds, 222 - Conjugation and isolation, 223 - Aromatic hydrocarbons, 226 - Conjugated ketones--quinone, 229 -Nitro and nitroso compounds, 230 - Azo compounds, 231 - Dyes, 231 -Use and specificity of electronic spectra, 233
Infra-red Correlations. . . . . . . . . . . . . . . . . . . . Characteristic group frequencies, 238 - Use of group frequency correlations, 240 - Specificity of infra-red spectra, 243
Raman Correla tions . . . . . . . . . . . Aqueous solutions, 245 - Non-aqueous solutions, 247
Microwave Correlations . . . . . . . . . . . . . . . . . Nuclear Magnetic Resonance . . . . . . . . ..... .
Magnetic dipole interaction, 249 - N.m.r . in liquids and gases, 252 - Chemical shift, 252 - Correlations, 254 - Electron-coupled nuclear spin interactions, 256 - N .m.r. fingerprints, 261
Intramolecular Perturbations . . . . . . . . . . . . . . . . Electronic spectra, 262 - Vibrational spectra, 263
Complexes and Ionic Association . . . . . . . . . . . . . . Crystal field theory, 267 - Selection rules, 272 - Spectrochemical series, 273 - Ligand field theory, 273 - Charge-transfer spectra, 274 - Chargetransfer spectra of ions in solution, 275 - Ionic association-complex ions, 276 - lonic association-ion pairs, 278 - Anions, 279
Intermolecular Perturbations . . . . . . . . . . . . . . . . Change of state, 280 - Change of symmetry, 281 - Solvent effects in electronic spectra, 282 - Solvent effects in vibration spectra, 283 - Hydrogen bonding, 284 - Solvent effects in nuclear magnetic resonance, 285 - Chemical exchange, 285
References . . . . . . . . . . . . . . . . . . . . . . . . .
CHAPTER 5. lNTENSITY • • • • • • • . • • . • • . • • • • • •
Concentration Dependence . . . . . . . . . . . . . . . . . Emission spectrophotometry, 290 - Atomic absorption spectroscopy, 292 -Absorption spectrophotometry, 292 - Beer's law, 293 - Analysis of mixtures, 294
218
219
244
262
266
280
290
290
X CONTENTS
Chemical Equilibria Determination of acid-base ionization constants, 296 - Quantitative Raman studies, 300 - Ionic association, 302 - Stoicheiometry of complex ions, 304 - Stability constants, 306
295
Kinetic Applications . . . . . . . . . . . . . . . . . . . . 308 Flash photolysis, 310
Population of Levels . . . . . . . . . . . . . . . . . . . . 313
Relaxation and resonance absorption, 314 - Rotational states, 316 - Vibra-tional and electronic absorption spectra, 318
Franck-Condon principle . . . . . . . . . . . . . . . . . . 318 Absorption, 319 - Emission, 320 - Dissociation processes: photochemistry, 321
Absolute Intensity . . . . . . . . . . . . . . . . . . . . . 323 Selection rules, 324 - Absolute intensity in absorption, 325 - Empirical correlations, 327
References. . 328
SUBJECT INDEX 331
Table I.
Table 2. Table 3.
Table 4· Table 5·
Table 6. Table 7. Table 8.
Table 9. Table 10. Table l I.
Table 12.
Table 13. Table 14. Table 15.
Table 16.
Table 17.
Table 18.
Table 19. Table 20. Table 21.
LIST OF T ABLES
Page
Correction to vacuurn of wavelength or wavenurnber. . . . . . 5 Wavelength, energy and frequency . . . . . . . . . . . . . . 8 Transparency of various optical rnaterials, and suitability for prisrns,
lenses and windows . . . . . . . . . . . . . . . . . . . . 23 Recornmended prism materials . . . . . . . . . . . . . . . . 26 Wavelengths (in air) and corresponding wavenumber (in vacuurn)
of mercury lines useful for calibration of spectrometers 44 Molar decadic extinction coefficien t . . . . . . . . . . . . . . 48 Verification of Ritz' combination principle. . . . . . . . . . . 85 Spin quanturn number and magnetic moment of sorne cornrnon
particles . . . . . . . . . . . . . . . . . . . . . . . . . l 06 Operation of Pauli's principle when n = I, 2 and 3 . . . . . . l 14 Operation of Pauli's principle in relativistic (n, k, m) atomic states II5 Part of Deslandres Table for the fourth positive group of CO, with
AG and LlG1 values . . . . . . . . . . . . . . . . . . . . 142 Vibrations parameters frorn emission spectra of sorne diatomic
molecules. . . . . . . . . . . . . . • . . . . . . . . . . 145 Character table for the point group C1v. • • • • • • • . • • • 167 Spectral activity of various configurations of XYZ, XY2 , XY3 178 Rotational constants for sorne diatomic and linear molecules from
pure rotational transitions in the Raman effect and microwave absorption . . . . . . . . . . . . . . . . . . . . . . 192
Rotational constants for some symmetric top molecules by the Rarnan and rnicrowave methods . . . . . . . . . . . . . . 195
Rotational constants for some asymmetric top molecules (rnicro-wave absorption) . . . . . . . . . . . . . . . . . . . . . 197
Comparison of values of rotational constants and dirnensions ob-tained by various spectroscopic rnethods . . . 209
Some representative group stretching frequencies. . . . . . . . 239 Chemical shifts for protons in various positions . . . . . . . . 255 N urnerical values of e - 4 E / kT for various LI E and various temperatures 3 l 3
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