BIRD (blackbody infrared radiative dissociation): Evolution, principles, and applications

I. Introduction 128 II. Brief History of the Development of BIRD 129 1. Dissociation by Ambient Radiation 129 2. The Rapid‐Exchange Limit 129 III. Experimental Approaches 130 IV. Fundamental Principles and Approaches to Interpretation 131 A. Kinetics Considerations 132 B. Large Molecules 134 1. When Is the Large‐Molecules Limit Achieved? 135 2. Small Molecules 137 3. Intermediate Size 138 V. Examples and Applications 140 A. Proton‐Bound Dimers 140 B. Solvent Detachment Studies 142 1. Small Solvated Ions 142 2. Deuteration Effects 142 3. Hydrated Metal Ions 143 4. Non‐Aqueous Solvents: Ru(bipy) +2 3 Complexes 143 C. Silanes 145 D. Zwitterions and Salt Bridges 146 E. Metal‐Cationized Amino Acids 147 F. Macrocycles 148 1. Iron Porphyrin Complexes 148 2. Hemoglobin/Myoglobin 148 G. Nucleotides and Oligonucleotides 149 H. Protein and Polypeptide Ions 149 I. Protein Complexes 149 J. Informative Fragmentations by BIRD Excitation 149 K. Analyzing Ion Mixtures 150 VI. Water‐Cluster Ions 150 VII. Extensions and Analogs to BIRD for Activation Energy Measurement 151 A. High‐Pressure Thermal Dissociation 152 1. Quadrupole Trap 152 2. Hot Reaction Zones in the Ion Source 152 B. Hot Filament Quasi‐BIRD 153 C. Laser IRMPD 154 D. Conclusion 154 References 155 Blackbody infrared radiative dissociation (BIRD) describes the observation of ion‐dissociation reactions at essentially zero pressure by the ambient blackbody radiation field, which is usually studied in the ion‐trapping ion cyclotron resonance (ICR) mass spectrometer. A brief summary of the historical context and evolution is provided. Focussing on the quantitative observation of the temperature dependence of BIRD rates, methods are developed for connecting BIRD observations with activation parameters and dissociation thermochemistry. Three regimes are differentiated and described, comprising large molecules, small molecules, and intermediate‐sized molecules. The different approaches to interpreting BIRD kinetics in those three regimes are discussed. In less than a decade since its inception, this approach to studying gas‐phase ions has spread over a wide variety of applications, which are surveyed. Some major areas of activity are: the characterization of solvent–molecule detachment from solvated ions; dissociation reactions of biomolecules (polypeptides, oligonucleotides, complexes involving polysaccharides) and the structural information to be deduced from them; and dissociations of proton‐bound and metal–ion‐containing complexes. Studies of blackbody‐radiation‐driven evaporation of water molecules from large water‐cluster ions are surveyed briefly. Several techniques related to BIRD are noted, including collisional dissociation in the FT‐ICR ion trap; high‐pressure thermal dissociation in quadrupole ion traps and in heated inlet capillary regions; hot‐filament‐assisted dissociation; and infrared multiphoton dissociation (IRMPD).