Stepwise laser photoionization of molecules in a mass spectrometer: a new method for probing and detection of polyatomic molecules

Abstract

Laser spectroscopy and kinetic mass spectrometry of polyatomic isolated molecules have been carried out by using stepwise laser ionization of molecules in a mass spectrometer. The optical absorption spectrum of NO(2) has been recorded, for example, by using pulsed dye-laser excitation and H(2) vacuum-ultraviolet laser ionization of molecules. The kinetics of excited electron states and of the production of molecular and fragmented ions of some polyatomic molecules have been investigated with high temporal resolution. The sensitivity achieved is 10(-10) cm(-1) of the absorption coefficient and 10(9) (10(5)) molecules in the ground (electronically excited) state in the irradiated volume.

Short pulse laser mass spectrometry of nitrotoluenes: ionization and fragmentation behavior

“…Ledingham and coworkers used femtosecond laser pulses at wavelengths of 375 and 750 nm for the investigation of several nitro molecules, including nitrobenzenes, as well as the three isomers of nitrotoluene, and could verify this observation 17,. 23 For the nitrotoluenes they were able to detect isomer‐specific fragmentation channels such as the OH loss in o‐nitrotoluene, a process which has been extensively studied,24–27 and the NO loss in the para isomer. It is obvious that such findings are of great importance for the analytical applications of laser mass spectrometry.…”

Frequency-comb spectroscopy on pure quantum states of a single molecular ion

“…Laser cooling and trapping [1-3], which revolutionized atomic physics, have enabled formation of molecules from cold atoms [4] and precision molecular spectroscopy [5]. Direct laser cooling of molecules shows promise for species with advantageous level structures that only require a few laser wavelengths [6-8], but is infeasible for the vast majority of molecules.Furthermore, even with trapped and cooled molecules [9], commonly used detection methods, such as state-dependent photo-dissociation or ionization [10,11], destroy the molecules under study, making them unavailable for further manipulation.In this work, we perform high resolution spectroscopy on rotational states of a molecular ion using methods that are generally applicable to a broad range of molecular ions, which are readily trapped in electromagnetic potentials [12] and cooled by coupling to co-trapped atomic ions amenable to laser cooling [13,14]. The long interrogation times and low translational temperature enabled by trapping and sympathetic cooling lead to high resolution [15], which has, among other advances, enabled the most stringent test of fundamental theory carried out by molecular ions [16].…”

State-specific detection of trapped HfF+ by photodissociation

“…The efficiency shortcoming of LIF can be alleviated if the molecules that occupy the quantum state of interest can be counted more directly, by taking advantage of high quantum efficiency ion detectors and easy manipulation of ion trajectories so that the ion detectors effectively subtend 4π solid angle. Resonanceenhanced multiphoton ionization (REMPI), which allowed detection of individual neutral molecules [11,12], has been utilized more recently for the efficient measurement of molecular quantum state populations. For detecting level population in molecular ions, the difficulty of efficiently and controllably removing the second electron makes REMPI a challenging technique to apply.…”