Multiphoton ionisation

Fast atom bombardment (FAB) Plasma desorption (PD) Liquid secondary-ion mass spectrometry (LSIMS) Thermospray (TSP)/plasmaspray (PSP) Electrohydrodynamic ionisation (EHI) Multiphoton ionisation (MPI) Atmospheric pressure chemical ionisation (APCI) Electrospray ionisation (ESI) Ion spray (ISP) Matrix-assisted laser desorption/ionisation (MALDI) Atmospheric pressure photoionisation (APPI) Triple quadrupole (QQQ) Four sector (EBEB) Hybrid (EBQQ) Hybrid (EB-ToF, Q-ToF) Tandem ToF-ToF Photomultiplier... 

Enhanced molecular ion implies reduced matrix interference. An SMB-El mass spectrum usually provides information comparable to field ionisation, but fragmentation can be promoted through increase of the electron energy. For many compounds the sensitivity of HSI can be up to 100 times that of El. Aromatics are ionised with a much greater efficiency than saturated compounds. Supersonic molecular beams are used in mass spectrometry in conjunction with GC-MS [44], LC-MS [45] and laser-induced multiphoton ionisation followed by time-of-flight analysis [46]. 

Other MS-fingerprinting techniques that are in commercial development are based on atmospheric pressure ionisation (API), resonance-enhanced multiphoton ionisation (REMPI) TOE and proton-transfer reaction (PTR). They are rapid, sensitive and specific and allow measurements in real time and may play an increasingly important role in the future development of electronic noses and tongues. 

MOS metal oxide sensor, MOSFET metal oxide semiconductor field-effect transistor, IR infrared, CP conducting polymer, QMS quartz crystal microbalance, IMS ion mobility spectrometry, BAW bulk acoustic wave, MS mass spectrometry, SAW siuface acoustic wave, REMPI-TOFMS resonance-enhanced multiphoton ionisation time-of-flight mass spectrometry... 

Fig. 15.14 Analytical techniques for time-resolved headspace analysis. An electronic nose can be used as a low-cost process-monitoring device, where chemical information is not mandatory. Electron impact ionisation mass spectrometry (EI-MS) adds sensitivity, speed and some chemical information. Yet, owing to the hard ionisation mode, most chemical information is lost. Proton-transfer-reaction MS (PTR-MS) is a sensitive one-dimensional method, which provides characteristic headspace profiles (detailed fingerprints) and chemical information. Finally, resonance-enhanced multiphoton ionisation (REMPI) TOFMS combines selective ionisation and mass separation and hence represents a two-dimensional method. (Adapted from [190])...

Resonance-Enhanced Multiphoton Ionisation Time-of-Flight Mass Spectrometry... 

Zewail acknowledged early on that he was inspired to work in the dynamics area by amongst others, George Porter s development of fast reaction techniques, viz. Flash Photolysis which is reported elsewhere in this volume. In the early experiments outlined in the present paper, three detection techniques were employed time-correlated single photon counting, with 30-50 ps time resolution streak camera detection of fluorescence, with 10 ps resolution, and multiphoton ionisation with resolution determined by the pulse width of the laser, 1 or 15 ps. 

Photodissociation yields of UF have been measured as a function of incidient light intensity in the presence of various additives,225 nd multiphoton ionisation of UF as a probe of laser-induced dissociation of UF, has been investigated using an... 

Fig. 9.2. Excitations schemes for resonantly enhanced multiphoton ionisation using three and four photons (schematic) (after J.-P. Connerade and A.M. Lane [385]).

P.E. Coleman, P.L. Knight, K. Burnett, Laser-induced continuum structure in multiphoton ionisation, Opt. Commun. 42 (1982) 171. 

D. Feldman, G. Otto, D. Petring, K.H. Welge, Resonances in the multiphoton ionisation spectrum of sodium atoms induced by a second strong laser field, J.Phys.B 19(1986)269. 

The use of resonance enhanced multiphoton ionisation (REMPI) spectroscopy Hnked to time of flight mass spectroscopy has been demonstrated in on-Hne monitoring of combustion by-products in industrial flue gases [14] and in a research project dedicated to the analysis of coffee roasting processes [15]. REMPI is a highly... 

The competition between dissociation and fluorescence produces such a dramatic effect in this case because the radiative lifetime is very long (- 23 ysec). The C state of H2O furnishes a very different example. The photodissociation dynamics of this state have been probed using multiphoton excitation, with detection either of ions or of fluorescence. The 3+1 resonance enhanced multiphoton ionisation spectra of the C states of H2O and D2O are dominated by levels with low K, and particularly (Ashfold, Bayley and Dixon 1984). The two-... 

The product state distribution can be measured directly, for example by laser induced fluorescence (LIF) or resonance enhanced multiphoton ionisation (REMPI). Both of these techniques yield the quantum specific density of AB molecules that are created in the dissociation process. However, these methods can be applied only to a limited number of molecules. Whereas LIF is essentially restricted to a few diatomic molecules, REMPI allows in a few favoured cases also the state selective detection of larger molecules. 

T. Baumert, M. Grosser, R. Thalweiser, G. Gerber, Femtosecond time-resolved molecular multiphoton ionisation the Na2 system. Phys. Rev. Lett. 67,3753 (1991)... 

Although not fully exploited because of the high diversity and complexity of laser experiments the introduction of multiphoton ionisation into mass spectrometry significantly expanded the applicability of this tool in the analysis of complex gas mixtures as the polluted atmosphere. Molecular specificity as obtained in high resolution vibrational spectroscopy combined with high sensitivity as known for ion counting methods makes this new technique unique in untangling reaction mechanisms [15, 19,20,24]. 

Mass spectrometric in-situ determination of NO2 in gas mixtures by resonance enhanced multiphoton ionisation,... 

Figure 6 Positive ion mass spectrum of high-purity GaAs recorded with TOF-LMMS without (A) and with (B) postionization. (Reprinted from Schueler B and Odom R (1987) Nonresonant multiphoton ionisation of the neutrals ablated In laser microprobe mass spectrometry analysis of GaAs and Hgo.78Cdo.22Te. Journal of Applied Physics 61 4652-4661.)...

Gasmi K, Al-Tuwirqi RM, Skowronek S, Telle HH, Gonzalez Urena A. 2003. Rotationally resolved (1 + 1 ) resonance-enhanced multiphoton ionisation (REMPI) of CaR (R = H,D) in supersonic... 

Cox and co-workers [179] analysed PS/polyvinyl methyl ether blends by coincidence counting ToF mass spectrometry. This technique gave information on the chemical and spatial relationships between secondary ions. Thompson [180] carried out a quantitative surface analysis of organic polymer blends (e.g., miscible polycarbonate/PS blends) using ToF-SIMS. Lin and co-workers [181] used supersonic beam/multiphoton ionisation/ToF mass spectrometry to analyse photoablation products resulting from styrene-containing polymers snch as styrene-bntadiene, ABS, and PS foams. Photoablation products were examined by snpersonic beam spectrometry and the results were compared with those obtained by thermal decomposition. 

Pulsed visible laser photolysis of triethylboron, hexamethylaluminiun, trimethylgalliuffl and trimethylindlum multiphoton ionisation spectra of aluminium, gallium uld Indlun atoms, S.A.Mltchell and P.A.Hackett, J. Chem. 

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