Multi-photon dissociation

Uranium enrichment using LIS has been exhaustively studied and the conceptual outlines of two different methods can be found in the open literature. These methods are multi-photon dissociation of UF6 (SILEX, or Separation of Isotopes by Laser Excitation) and laser excitation of monatomic uranium vapor (Atomic Vapor Laser Isotope Separation, or AVLIS). Following an enormous investment, AVLIS was used by the United States DOE in the 1980s and early 1990s, but due to the present oversupply of separated uranium, the plant has been shut down. 

Goolsby, B.J. Brodbelt, J.S. Analysis of protonated and alkali metal cationized aminoglycoside antibiotics by collision-activated dissociation and infrared multi-photon dissociation in the quadrupole ion trap. J. Mass Spectrom., 35,1011-1024 (2000). 

In all three instrumental configurations, it is possible to induce decomposition of the ion trapped inside the ICR cell not only by collisional experiments, but also by interaction with slow electrons (electron capture dissociation, ECD) or by irradiation with an infrared (IR) laser beam (infrared multi photon dissociations, IRMPD). Experiments of this type (mainly devoted to polypeptide identification) allow to maintain the high-vacuum conditions inside the ICR cell, which are necessary to achieve the high-resolution conditions. 

Hughes, R.J. March, R.E. Young, A.B. Multi-photon dissociation of ions derived from 2-propanoI in a QUISTOR with low-power cw infrared-laser radiation. Int. J. Mass Spectrom. Ion Processes. 1982,42, 255-263. 

M. C. Crowe and J. S. Brodbelt, Infrared multi-photon dissociation (IRMPD) and collisionally activated dissociation of peptides in a quadrupole ion trap (QIT) with selective IRMPD of phosphopeptides, J. Am. Soc. Mass Spectrom. 15, 1581-1592, (2004). 

J. W. Flora and D. C. Muddiman, Selective, sensitive, and rapid phosphopeptide identification in enzymatic digests using ESI-FTICR-MS with infrared multi-photon dissociation. Anal. Chem. 73, 3305-3311 (2001). 

The multi-photon dissociation process is illustrated in Fig. 10.34. Because of the anharmonicity of the vibrational potential a photon energy that is resonant in the first vibrational step will successively pull out of resonance higher up in the vibrational energy level ladder. However, the molecule can be excited in a multi-photon process (Sect.9.1.3c) until it is dissociated. SFg then disintegrates into SF5 and F. By making the first step resonant for one isotopic molecule the probability of subsequent dissociation for this molecular species is significantly increased. 

Abstract In this chapter we review recent advances in theoretical methods to understand and rationalize anharmonic vibrational spectroscopy (IR-MPD and IR-PD) and collision induced dissociations (CID) in the gas phase. We focused our attention on the application of molecular dynamics-based methods. DFT-based molecular dynamics was shown to be able to reproduce InfraRed Multi-Photon Dissociation (IR-MPD) and InfraRed Pre-Dissociation (IR-PD) action spectroscopy experiments, and help assign the vibrational bands, taking into account finite temperature, conformational dynamics, and various anharmonicities. Crucial examples of dynamical vibrational spectroscopy are given on the protonated AlanH" series (related to IR-MPD in the 800-4,0(X) cm domain), ionic clusters (related to IR-PD in the 3,000-4,(XX) cm region), and neutral peptides (related to IR-MPD in the far-lR). We give examples from simple (e.g., cationized urea) to more complex (e.g., peptides and carbohydrates) molecular systems where molecular dynamics was particularly suited to understanding CID experiments. 

Bomse, D. S. Woodin, R. L. Beauchamp, J. L. Molecular activation with low-intensity Cw infrared-laser radiation—Multi-photon dissociation of ions... 

The absorption of far-IR photons can be detected by the messenger method, which is based on forced evaporation of a weakly-bound ligand from the cluster complex upon the absorption of a small number of IR photons. The messenger method assumes that only the metal cluster acts as a chromophore while the detached atomic or molecular ligand merely delivers the message about the absorption event without perturbing the structural properties of the cluster. This assumption is fulfilled for most transition metal clusters complexed with rare gas atoms. In combination with density functional theory calculations, the experimental IR (multi) photon dissociation, IR-(M)PD, spectra often enable an unambiguous determination of the clusters structure. 

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