REMPI
Definition and meaning of REMPI in chemistry.
Resonance-enhanced multiphoton ionization is an advanced laser spectroscopy technique that involves the simultaneous or highly sequential absorption of multiple photons to successfully ionize an atom or molecule by passing through a specific intermediate electronic state. This specialized analytical method provides exceptionally highly sensitive and incredibly selective detection of minuscule trace species within complex gas mixtures.
In more detail
In a typical analytical REMPI experiment, a powerful tunable laser is carefully used to quickly excite the chosen target molecule to a resonant intermediate quantum state by absorbing one or more initial photons. From this transient excited state, the rapid absorption of additional incoming photons provides more than enough kinetic energy to completely overcome the first ionization potential, vigorously ejecting an electron and creating a freely detectable positive ion. Because the exact energy of the intermediate resonant state is entirely unique to each specific chemical molecule, REMPI offers truly exceptional spectral resolution and unparalleled chemical species selectivity. The resulting charged ions are then typically efficiently detected using sophisticated mass spectrometry equipment, creating an incredibly powerful analytical tool for studying complex chemical reaction dynamics and performing highly sensitive trace gas analysis.
Key facts
| Field | Physical Chemistry |
|---|---|
| Core Mechanism | Ionization proceeding via a specific resonant intermediate state |
| Primary Advantage | Extremely high analytical sensitivity and chemical species selectivity |
A very common analytical scheme is 1+1 REMPI, where exactly one photon initially excites a molecule to an intermediate excited state, and a subsequent second photon of the exact same wavelength successfully ionizes it, a process often used to precisely detect trace nitric oxide (NO) in combustion diagnostics.
Frequently asked questions
Why exactly is this technique called 'resonance-enhanced'?
The ionization efficiency is vastly enhanced when the combined energy of the incident photons perfectly matches the exact energy difference between the ground state and a specific, real intermediate state of the molecule.