Multiple-photon spectroscopy

There are several other interesting topics in quantum optics which we would like to be able to study. For example, we would like model problems in double resonance spectroscopy, where there are two electromagnetic fields with possibly different polarizations simultaneously interacting with a molecule. This problem resembles the multiple photon excitation problem in that there is population migration along ladders of states, but in this case there can be a vastly larger number of quantum levels to treat — on the order of 2(2J+1). At room temperature, the most probable value of J for SF is about 60, which implies a 250 state calculation. 

Coherent anti-Stokes Raman spectroscopy (CARS) Unlike spontaneous Raman emission, the magnitude of signal in CARS is number of orders stronger as multiple photons are employed to address the molecular vibrations, resulting in production of a signal in which the emitted waves are coherent with one... 

Iron clusters exhibit facile chemisorption toward methanol, the reaction proceeding with little or no cluster-size selectivity. An interesting feature of this system is that the chemisorption rate constants are nearly identical toward various isotopic sjjecies (CH3OH, CH30D,CD3 0H). If dissociation of a C—H or O—H bond was the initial step, then this should be manifested in an observable kinetic isotope effect. Thus the initial chemisorption step most likely involves the lone-pair orbital localized on the oxygen atom. More extensive studies of the chemistry of the Fe methanol system have been explored using infrared multiple-photon dissociation spectroscopy. These results are discussed in detail in Section Vlll. 

Vibrational spectroscopy is an important probe used to determine the bonding and structural properties of molecules. Powerful techniques such as electron energy loss spectroscopy (EELS) have been developed, which allow one to obtain the vibrational properties of molecules chemisorbed upon surfaces. Due to low concentration, the highly reactive nature of the clusters, and the large number of possible species which are typically present in the cluster beams used to date, unconventional techniques are required in order to obtain spectroscopic information. One unconventional but powerful technique, infrared multiple photon dissociation (IRMPD), has recently been applied to the study of the vibrational properties of gas-phase metal clusters upon which one or more molecules have been chemisorbed. This same technique, IRMPD, has previously been used to obtain the vibrational spectra of ions, species for which it is difficult to apply conventional absorption techniques. 

As mentioned in Section 9.2, there is an important distinction between action spectroscopies based on the absorption of multiple photons, as is possible with FEL excitation, and those based on single photon absorption, such as messenger spectroscopy [26,27], laser-induced reaction spectroscopy [73] or indeed direct absorption experiments. When the signal (in this case, the depletion of the parent ion and creation of product ious) depends on the absorption of multiple photons, the signal intensity may not be compared directly to computed linear (single-photon) absorption spectra, as is the normal fashion. There are several reasons why intensities may differ. Thus, baudpositiou (frequency) is considered usually to be more reliable than band intensity when comparing computed and experimentally-measured spectra. 

Oomens, J. Sartakov, B.G. Meijer, G. VonHelden, G. Gas-phase infrared multiple photon dissociation spectroscopy of mass-selected molecular ions. Int. J. Mass Spectrom. 2006, 254,1-19. 

Polfer NC. Infrared multiple photon dissociation spectroscopy of trapped ions. Chem Soc Rev. 2011 40 2211-21. 

Citir M, Steimett EMS, Oomens J, Steill JD, Rodgers MX, Armentrout PB. Infrared multiple photon dissociation spectroscopy of cationized cysteine effects of metal cation size on gas-phase conformation. Int J Mass Spectrom. 2010 297 9-17. 

Nucleotides are covered elsewhere in this volume but worthy of mention is the cyclic 3, 5 -adenosine monophosphate anion (cAMP-H) , generated in gaseous species by electrospray ionization (ESI) and stored in an ion-trap mass spectrometer. This has been investigated by mass-resolved infrared multiple photon dissociation (IRMPD) spectroscopy in the 900 1800 cm fingerprint range using the powerful and continuously-tunable radiation from a free electron laser. Further details of this IRMPD application are given in the mass spectrometry section later. 

The types of action spectroscopy presented in this book include IR-UV ion dip spectroscopy for neutral species and Infrared Multiple Photon Dissociation... 

Wu RH, McMahon TB (2007) Infrared multiple photon dissociation spectroscopy as structural confirmation for GlyGlyGlyH(-l-) and AlaAlaAlaH(-t) in the gas phase. Evidence for amide oxygen as the protonation site. J Am Chem Soc 129 11312... 

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