Resonance ionization

Photon beams from a tunable laser are used to selectively excite and promote cloud of atoms or molecules from ground state to higher excited states in resonance ionization.

Resonance ionization is a process in optical physics used to excite a specific atom (or molecule) beyond its ionization potential to form an ion using a beam of photons irradiated from a pulsed laser light.[1] In resonance ionization, the absorption or emission properties of the emitted photons are not considered, rather only the resulting excited ions are mass-selected, detected and measured.[2] Depending on the laser light source used, one electron can be removed from each atom so that resonance ionization produces an efficient selectivity in two ways: elemental selectivity in ionization and isotopic selectivity in measurement.[2][3][4]

During resonance ionization, an ion gun creates a cloud of atoms and molecules from a gas-phase sample surface and a tunable laser is used to fire a beam of photons at the cloud of particles emanating from the sample (analyte).

An initial photon from this beam is absorbed by one of the sample atoms, exciting one of the atom's electrons to an intermediate excited state. A second photon then ionizes the same atom from the intermediate state such that its high energy level causes it to be ejected from its orbital; the result is a packet of positively charged ions which are then delivered to a mass analyzer.[5][6]

Resonance ionization contrasts with resonance-enhanced multiphoton ionization (REMPI) in that the latter is neither selective nor efficient since resonances are seldom used to prevent interference. Also, resonance ionization is used for an atomic (elemental) analyte, whereas REMPI is used for a molecular analyte.[7]

The analytical technique on which the process of resonance ionization is based is termed resonance ionization mass spectrometry (RIMS). RIMS is derived from the original method, resonance ionization spectroscopy (RIS), which was initially being used to detect single atoms with better time resolution.[8] RIMS has proved useful in the investigation of radioactive isotopes (such as for studying rare fleeting isotopes produced in high-energy collisions), trace analysis (such as for discovering impurities in highly pure materials), atomic spectroscopy (such as for detecting low-content materials in biological samples), and for applications in which high levels of sensitivity and elemental selectivity are desired.

  1. ^ Samuel Hurst, G.; Letokhov, Vladilen S. (1994). "Resonance Ionization Spectroscopy". Physics Today. 47 (10): 38–45. Bibcode:1994PhT....47j..38S. doi:10.1063/1.881420. ISSN 0031-9228.
  2. ^ a b Fassett, J.D.; Travis, J.C. (1988). "Analytical applications of resonance ionization mass spectrometry (RIMS)". Spectrochimica Acta Part B: Atomic Spectroscopy. 43 (12): 1409–1422. doi:10.1016/0584-8547(88)80180-0. ISSN 0584-8547.
  3. ^ Fassett, J. D.; Travis, J. C.; Moore, L. J.; Lytle, F. E. (1983-04-01). "Atomic ion formation and measurement with resonance ionization mass spectrometry". Analytical Chemistry. 55 (4): 765–770. doi:10.1021/ac00255a040. ISSN 0003-2700.
  4. ^ Köster, U. (2002). "Resonance ionization laser ion sources". Nuclear Physics A. 701 (1–4): 441–451. Bibcode:2002NuPhA.701..441K. doi:10.1016/s0375-9474(01)01625-6.
  5. ^ Hurst, G. S.; Kutschera, W.; Oeschger, H.; Korschinck, G.; Donahue, D. S.; Litherland, A. E.; Ledingham, K.; Henning, W. (1987). "Detection of Single Atoms by Resonance Ionization Spectroscopy [and Discussion]" (PDF). Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 323 (1569): 155–170. doi:10.1098/rsta.1987.0079. ISSN 1364-503X.
  6. ^ Wendt, K.; Blaum, K.; Bushaw, B. A.; Grüning, C.; Horn, R.; Huber, G.; Kratz, J. V.; Kunz, P.; Müller, P. (1999-07-01). "Recent developments in and applications of resonance ionization mass spectrometry". Fresenius' Journal of Analytical Chemistry. 364 (5): 471–477. doi:10.1007/s002160051370. ISSN 0937-0633.
  7. ^ Dass, Chhabil (2007). "Chapter 7: Inorganic Mass Spectrometry". In Desiderio, Dominic M.; Nibbering, Nico M. (eds.). Fundamentals of Contemporary Mass Spectrometry (1st ed.). John Wiley & Sons, Inc. pp. 273–275. ISBN 978-0471682295.
  8. ^ Young, J. P.; Shaw, R. W.; Smith, D. H. (2008). "Resonance ionization mass spectrometry". Analytical Chemistry. 61 (22): 1271A–1279A. doi:10.1021/ac00197a002. ISSN 0003-2700.