IR : Theory and Practice of Infrared Spectroscopy

The first edition of this text was written primarily by one of the present authors (HAS), with a chapter on instrumentation contributed by a second (NLA). The volume was well received, and to keep the text up-to-date a second edition was planned. For this second edition, a third author (WEK) was invited, whose background complemented that of the other two. Each of the authors was assigned several chapters as his primary task while the complete manuscript remained the second­ ary responsibility of all three. It is hoped that this approach has resulted in a work that is even more thorough than the first edition in covering the basic concepts of infrared spectroscopy. NELSON L. ALPERT WILLIAM E. KEISER HERMAN A. SZYMANSKI v PREFACE TO THE FIRST EDITION My experience with the many infrared spectroscopy institutes held at Canisius College and many discussions with both beginners and experienced practitioners in infrared spectroscopy have convinced me that there is a need for an introductory text devoted entirely to infrared spectroscopy, a text which can be utilized even by those who approach this study with only a limited background. This volume sprang from that conviction. It is intended for all who wish to use infrared spec­ troscopy in research - especially chemists doing structural work - in routine control work, in industrial development, or in medical appli­ cations or those military applications where it is employed as an analytical tool.

1 Introduction to Infrared Spectroscopy.- 1.1. Units.- 1.2. Regions of Electromagnetic Radiation.- 1.3. The Infrared Spectrum of a Compound.- 1.4. Atmospheric Absorptions.- 2 Instruments.- 2.1. Description.- 2.2. Operating Variables.- 2.2A. Resolution.- 2.2B. Photometric Accuracy.- 2.2C. Quantitative Relations Between Operating Variables.- 2.3. Components of Infrared Spectrophotometers.- 2.3A. Sources.- 2.3B. Photometers and Photometric Systems.- 2.3C. Dispersing Elements.- 2.3D. Detectors.- 2.3E. Amplifiers and Recorders.- 2.3F. Polarizers.- 2.4. Special Operating Features.- 2.4A. Variation of Basic System Parameters.- 2.4B. Variation of Recording Parameters.- 2.4C. Optimization of Scan Time.- 2.4D. Compensation for Nonprogrammed Energy Losses.- 2.5. Available Instruments and Their Specifications.- 2.6. The Computer Revolution.- References.- 3 Accessories.- 3.1. Crystals.- 3.2. Gas Cells.- 3.3. Liquid Cells.- 3.4. KBr-Pellet Accessories.- 3.5. Beam Condensers.- 3.6. Polarizers.- 3.7. Specular Reflectance.- 3.8. ATR.- 3.9. Miscellany.- References.- 4 Theoretical Considerations in Infrared Spectroscopy.- 4.1. Notation.- 4.2. Diatomic Molecules.- 4.2A. Absorption of Infrared Radiation.- 4.2B. Relationship Between Band Contours and Vibrational-Rotational Energy.- 4.2C. Mathematical Relations for Rotational and Vibrational Energy.- 4.2D. The Intensity Distribution of a Band.- 4.3. Polyatomic Molecules.- 4.3A. The Relationship Between Observed Absorption Bands and Motions of the Atoms in a Molecule.- 4.3B. The Relationship Between Dipole Moment Changes and Infrared Absorption Bands.- 4.3C. Vibrations for Molecules Containing Four or More Atoms.- 4.4. The Relationship Between Symmetry of Molecules and Observed Absorption Bands.- 4.4A. Introduction.- 4.4B. Point Symmetry and Point Groups.- 4.4C. Point Groups for Various Molecules.- 4.5. Character Tables and Types (Species) of Vibrations.- 4.5A. Species for Point Groups C1, C2, Cs, and Ci.- 4.5B. Species for Point Groups C2v, C2h, and D2.- 4.5C. Species of the C2h Point Group.- 4.5D. Species of Vibration for C3v and D3 Groups.- 4.5E. Species of Vibration for Other Cnv, Groups.- 4.5F. Species of Vibration of Other Groups.- 4.6. Molecules with Centers of Symmetry.- 4.7. Correlation of Species of Related Molecules.- 4.8. Calculation of Allowed Bands Using Group Theory.- 4.8A. Calculation of Allowed Fundamentals. The Character Table.- 4.8B. Calculation of the Allowed Combination Bands in the Infrared.- 4.8C. Calculation of the Allowed Overtone Bands in the Infrared.- 4.8D. Calculation of the Number of Allowed Infrared Fundamentals.- 4.9. Factors Influencing Band Positions and Band Contours in Polyatomic Molecules.- 4.9A. Fermi and Coriolis Perturbations.- 4.9B. Inversion Doubling.- 4.9C. Intensity Alternation of the Line Structure of Bands.- 4.9D. l-Type Doubling.- 4.10. Band Contours for Linear Molecules.- 4.11. The Method of Combination Differences Used to Obtain Rotational Constants of Diatomic and Linear Molecules.- 4.12. Vibrational-Rotational Energy Equations for the Symmetric Rotor.- 4.13. Analysis of the Ammonia Spectrum (Symmetric Rotor).- 4.14. Spherical Rotor Molecules.- 4.15. The Asymmetric Rotor.- 4.16. Spectral Analysis of Formaldehyde (Near Symmetric Rotor).- 4.16A. The 3–4 µ Region.- 4.16B. The 5.7 µ Region.- 4.16C. The 6–7 µ Region.- 4.16D. The 7.5–10 µ Region.- 4.17. Fundamental Frequencies of the Molecules CF2=CH2, CF2=CHD, and CF2=CD2.- 4.18. The Influence of Isotopic Substitution on Band Position.- 4.19. Conclusion.- References.- 5 The Use of Characteristic Group Frequencies in Structural Analysis.- 5.1. General Objectives.- 5.2. Definition of Group Frequencies.- 5.3. Group Frequencies and the Vibrational Analysis of a Molecule.- 5.3A. The Constancy of Spectral Positions of Group Frequencies.- 5.3B. Group Frequencies of M—H Structural Units.- 5.3C. Terminal Structural Groups such as C=O and Multiple-Bond Groups.- 5.3D. Group Frequencies of Units Where the Mass Factor Is Important.- 5.3E. Ring and Other Group Vibrations.- 5.3F. The Influence of Symmetry on Group Frequencies.- 5.3G. Summary.- 5.4. Group Frequencies of the CH3, CH2, and CH Structural Units.- 5.4A. Alkanes Containing the CH3 and CH2 Units.- 5.4B. Branched-Chain Hydrocarbons.- 5.4C. CH3 Groups Adjacent to Atoms Other than Saturated Carbon.- 5.4D. CH2 Groups Adjacent to Atoms Other than Saturated Carbon.- 5.4E. Saturated Ring Systems.- 5.4F. Groups Having Absorption Bands Which Interfere with Group Frequency Assignments of CH3 and CH2 Groups.- 5.4G. The Spectra of Compounds with CH3 and CH2 Groups.- 5.4H. CH3 and CH2 Group Frequencies in Alkenes.- 5.4I. CH3 and CH2 Group Frequencies in Aromatic Compounds.- 5.5. Group Frequencies Associated with Alkenes.- 5.5A. 1680–1580 cm?1 Region for Alkenes.- 5.5B. 970–660 cm?1 Region for Alkenes.- 5.5C. 3100–3000 cm?1 Region for the —C=C—H Group.- 5.5D. Interpretation of Spectra of Alkenes.- 5.6. Group Frequencies Associated with Alkynes.- 5.6A. Group Frequencies Associated with the Unit C=C—H.- 5.7. Characteristic Group Frequencies for Benzene Derivatives.- 5.7A. Aromatic CH Stretching Frequencies.- 5.7B. Benzene Ring Vibrations in the 2000–1660 cm?1 Region.- 5.7C. Aromatic Ring Frequencies in the 1600–1450 cm?1 Region.- 5.7D. Benzene Ring Vibrations in the 1225–950 cm?1 Region.- 5.7E. Group Frequencies of Benzene Derivatives in the 950–650 cm?1 Region.- 5.7F. Summary of Benzene Ring Group Frequencies.- 5.8. Vibrations of Pyridine and Its Derivatives.- 5.9. Group Frequencies Associated with the C=O Structural Unit.- 5.10. Group Frequencies Associated with the C—O—C and C—O—H Structural Units.- 5.11. Group Frequencies Associated with NH and CN Structural Units.- 5.12. Amide I Band.- 5.13. Amide II Band.- 5.14. Amide III, IV, V, and VI Bands.- 5.15. Group Frequencies for Fluorocarbons.- 5.16. Group Frequencies for the C=N, N=O, C?N, and Other Structural Units.- 5.17. Organic Molecules Coordinated to Inorganic Salts.- 5.18. Practice Interpretation of Spectra.- References.- 6 Quantitative Analysis.- 6.1. Beer’s Law.- 6.2. Analysis of a Series of Samples.- 6.3. Multicomponent Analysis.- 6.4. Solid Samples.- 6.5. Gas Samples.- 6.6. “One-Time” Analysis.- 6.7. Sources of Error.- 6.8. Noninterchangeability of Data.- 6.9. Measuring Absorbance.- 6.10. Accuracy.- 6.11. Other Techniques.- 6.12. Literature.- Reference.- 7 Sample-Handling Techniques.- 7.1. Gases.- 7.2. Liquids.- 7.3. Solids.- 7.4. Miscellany.- 7.5. Microsampling.- 7.6. Conclusions.- References.- 8 Spectra and Reference Library.- 8.1. General References to Infrared Spectroscopy.- 8.2. Government Publications.- 8.3. House Organs of Various Companies and Laboratories.- 8.4. Reference Spectrograms and Spectral Retrieval Systems.- 8.5. Abstracting Services and Bibliographies.- Appendixes.- Appendix 1. Additional References.- Appendix 2. Character Tables of the Most Important Point Groups.