Resonance Enchanced Multi-Photon Ionization (REMPI)

A REMPI experiment uses two lasers applied in sequence. The first laser promotes the molecules of interest into an excited electronic state. A second laser with sufficient energy to ionize the target molecules from the excited states and not the ground state is then fired after a typical delay of ~20 ns. The resulting ions are analysed using a time-of-flight (TOF) mass spectrometer equipped with a microchannel plate (MCP) detector. This technique allows the absorption spectra for many different radicals of different masses to be recorded all at once. However, only neutral species with suitable excited electronic states can be detected. Its greatest advantage lies in its mass-selectivity, which allows one to make an unambiguous assignment of the absorption features.

Transient species are produced either by an electrical discharge of a precursor gas diluted in an inert buffer, or through ablation of a solid precursor material (rod or disc), followed by supersonic expansion into vacuum. Various carbon chains have been studied using the REMPI apparatus, ranging from C₃H to HC₂₄H or C₁₈, and more recently, the metal terminated systems like MgC_2nH (n = 1-3).

Selected publications:

• Xiujuan Zhuang, Anh Le, Timothy C. Steimle, Ramya Nagarajan, Varun Gupta, and John P. Maier
  Phys. Chem. Chem. Phys., 12(45), 15018–15028, 2010.
  Visible Spectrum of Titanium Dioxide
  
• C. Apetrei, A.E.W. Knight, E. Chasovskikh, E.B. Jochnowitz, H. Ding, and J.P. Maier
  J. Chem. Phys., 131(6), 064305/1–7, 2009.
  Gas phase electronic spectrum of T-shaped AlC₂ radical
  
• Cristina Apetrei, Ramya Nagarajan, and John P. Maier
  J. Phys. Chem. A, 113(42), 11099–11100, 2009.
  Gas Phase 1¹Σ_u⁺ ← X ¹Σ_g⁺ Electronic Spectra of Polyacetylenes HC_2nH, n = 5–7
  
• Łukasz Chacaga, Evan B. Jochnowitz, Zohra Guennoun, Hongbin Ding, and John P. Maier
  Int. J. Mass Spectrom., 280(1–3), 174–178, 2009.
  The electronic gas-phase spectrum of B₃ radical revisited
  
• John P. Maier, Andrey E. Boguslavskiy, Hongbin Ding, Gordon A.H. Walker, and David A. Bohlender
  Astrophys. J., 640(1), 369–372, 2006.
  The Gas Phase Spectrum of Cyclic C₁₈ and the Diffuse Interstellar Bands