Dissociation multiple-photon

The Exxon data 7or iron with methanol also does not show size selective behavi or(52). The Exxon group has been able to show by infrared multiple photon dissociation that the 0-H bond breaks forming methoxy on these small iron c usters(3h). This is consistent with the behavior of methanol at room temperature on iron... 

T. D. Frigden, L. MacAleese, T. B. McMahon, J. Lemaire, and P. Maitre, Gas phase infrared multiple photon dissociation spectra of methanol, ethanol and propanol proton bound dimers, protonated propanol and the propanol/water proton bound dimer. Phys. Chem. Chem. Phys. 8, 955 966 (2006). 

Fragmentation of peptides can also be observed with FTICR instruments. Infrared multiple photon dissociation (IRMPD) and electron capture dissociation (ECD) have been introduced as two alternative dissociation methods to the low-energy CID method. The IRMPD method produces many fragments that make the spectrum very complex and difficult to interpret. Some of the fragment types observed with IRMPD are b and y type ions or these ions that have lost ammonia or water. However, most of them are not these types of fragment ions. 

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. 

Marling, J.B. Herman, I.P. Deuterium separation with 1400-fold single-step isotopic enrichment and high yield by C02-laser multiple-photon dissociation of 2,2-dichloro-l,l,l-trifluoroethane. Appl. Phys. Lett. 1979, 34, 439. 

Kaldor, K. Cox, D. M. "Energy Localization in CO2 Laser Driven Multiple Photon Dissociation," J. Chem. Phys., submitted for publication. 

Rate constants for reaction of the CH radical with a number of atomic and molecular collision partners have been reported, with multiple-photon dissociation of suitable precursor molecules using either infrared or ultraviolet " laser radiation used as the pulsed photolysis source, and laser-induced fluorescence near 431 nm employed as a sensitive time-resolved detection method. A similar technique has been used to measure removal rates of CH2 and CDj with... 

Here we report Doppler experiments carried out recently in our laboratory. Two kinds of studies have been made, both with the main objective to establish and investigate the potential of the method (1) first multiple-photon dissociation Doppler experiments under crossed-beam condition with CjHjCN and CH3NH2, and (2) first linewidth measurement in single vibrational-rotational levels of NO produced by one-photon dissociation of NO2 in bulk with unpolarized and polarized light, in connection with complete internal energy distribution measurements of the NO fragment. 

The C2 radical is produced by multiple-photon dissociation of CF3CCCF3 at 193 nm. Approximately 20 torr of helium is used to translationally and rotationally equilibrate the C2 with the bath gas. The dissociation produces both C2 and C2 and a significant amount of the C2 is vibrationally excited. Our experiments indicate that at these pressures helium is not effective at vibrationally quenching the C2, although the rapid rotational thermalization is clearly evident. For measurements of the reaction rates of C2, 1 2 mtorr of CF3CCCF3 is used with 20 torr of 99.99% helium and 0-0.8 torr of 99.99% O2. 

As mentioned earlier, CPMD simulations were carried out at 300K on deprotonated phosphorylated serine (p-ser-H) , and the resultant extracted spectrum correlates with the experimental IR spectrum obtained by the recently-developed InfraRed Multiple Photon Dissociation (IRMPD) technique, which was first described in this chapter in Volume 39. 

A wide variety of lasers have been used in combination with trapping mass spectrometers. Two lasers in particular are incorporated already into many commercial mass spectrometers the CO2 (X= 10.6 pm or 0.12 eV photon ) and nitrogen (X=337 nm or 3.68 eV photon ) lasers. The former is used for performing infrared multiple photon dissociation (IRMPD) experiments (mostly in ICR instruments, see Section 9.3) while the latter is used commonly in MALDl ionization sources. Other commonly-used lasers are Q-switched Nd YAG lasers (fundamental X= 1064 nm... 

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. 

Stephenson, J.L. Booth, M.M. Shalosky, J.A. Eyler, J.R. Yost, R.A. Infrared multiple-photon dissociation in the quadrupole ion-trap via a multipass optical arrangement. J. Am. Soc. Mass Spectrom. 1994,5, 886-893. 

Prison, G. van der Rest, G. Turecek, F. Besson, T. Lemaire, J. Maitre, P Chamot-Rooke, J. Structure of electron-capture dissociation fragments from charge-tagged peptides probed by tunable infrared multiple photon dissociation. J. Am. Chem. Soc. 2008, 130, 14916-14917. 

Atkins, C.G. Rajabi, K. GiUis, E.A.L. Fridgen, T.D. Infrared multiple photon dissociation spectra of proton- and sodium ion-bound glycine dimers in the N-H and O-H stretching region. J. Phys. Chem. A. 2008,112,10220-10225. 

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. 

---