Infrared photodissociation (IRPD) spectroscopy uses

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

radiation to break bonds in

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s, ( photodissociate), within a mass spectrometer. IRPD spectroscopy has been shown to use electron ionization, corona discharge, and

electrospray ionization Electrospray ionization (ESI) is a technique used in mass spectrometry to produce ions using an electrospray in which a high voltage is applied to a liquid to create an aerosol. It is especially useful in producing ions from macromolecules becaus ...

to obtain spectra of volatile and nonvolatile compounds. Ionized gases trapped in a

mass spectrometer Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is us ...

can be studied without the need of a solvent as in

infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...

History

Scientists began to wonder about the energetic of cluster formation early in the 19th century. Henry Eyring developed the activated-complex theory describing

kinetics Kinetics ( grc, κίνησις, , kinesis, ''movement'' or ''to move'') may refer to: Science and medicine * Kinetics (physics), the study of motion and its causes ** Rigid body kinetics, the study of the motion of rigid bodies * Chemical ki ...

of reactions. Interest in studying the weak interactions of molecules and ions(e.g. van der Waals) in clusters encouraged gas phase spectroscopy, in 1962 D.H. Rank studied weak interactions in the gas phase using traditional infrared spectroscopy. D.S. Bomse used IRPD with an ICR to study isotopic compounds in 1980 at California Institute of Technology. Spectroscopy for weak bonding clusters was limited by low cluster concentration and the variety of accessible cluster states. Cluster states vary in part due to frequent collisions with other species, to reduce collisions in gas phase IRPD forms clusters in low pressure ion traps (e.g. FT-ICR). Nitrogen and water were one of the first complexes studied with the aid of a mass spectrometer by A. Good at University of Alberta in the 1960s.

Instrumentation

Photodissociation is used to detect electromagnetic activity of ions, compounds, and clusters when spectroscopy cannot be directly applied. Low concentrations of

analyte An analyte, component (in clinical chemistry), or chemical species is a substance or chemical constituent that is of interest in an analytical procedure. The purest substances are referred to as analytes, such as 24 karat gold, NaCl, water, etc. ...

can be one inhibiting factor to spectroscopy esp. in the gas phase. Mass spectrometers,

time-of-flight Time of flight (ToF) is the measurement of the time taken by an object, particle or wave (be it acoustic, electromagnetic, etc.) to travel a distance through a medium. This information can then be used to measure velocity or path length, or as a w ...

and

ion cyclotron resonance Ion cyclotron resonance is a phenomenon related to the movement of ions in a magnetic field. It is used for accelerating ions in a cyclotron, and for measuring the masses of an ionized analyte in mass spectrometry, particularly with Fourier transfo ...

have been used to study hydrated ion clusters. Instruments are able to use ESI to effectively form hydrated ion clusters. Laser ablation and

corona discharge A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor (material), conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone e ...

have also been used to form ion clusters. Complexes are directed through a mass spectrometer where they are irradiated with infrared light, Nd:YAG laser.

Application

Infrared photodissociation spectroscopy maintains a powerful capability to study bond energies of

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. ...

es. IRPD can measure varying bond energies of compounds, including

dative bond In coordination chemistry, a coordinate covalent bond, also known as a dative bond, dipolar bond, or coordinate bond is a kind of two-center, two-electron covalent bond in which the two electrons derive from the same atom. The bonding of metal ...

s and coordination energies of molecular clusters. Structural information about analytes can acquired by using mass selectivity and interpreting fragmentation. 3D model hydrogen bonds in water

References

{{reflist Infrared Mass spectrometry Chemical bond properties Spectroscopy