Product Screening of Fast Reactions in IR-Laser-Heated Liquid Water Filaments in a Vacuum by Mass Spectrometry

Abstract

In the present article a novel approach for rapid product screening of fast reactions in IR-laser-heated liquid microbeams in a vacuum is highlighted. From absorbed energies, a shock wave analysis, high-speed laser stroboscopy, and thermodynamic data of high-temperature water the enthalpy, temperature, density, pressure, and the reaction time window for the hot water filament could be characterized. The experimental conditions (30 kbar, 1750 K, density approximately 1 g/cm3) present during the lifetime of the filament (20-30 ns) were extreme and provided a unique environment for high-temperature water chemistry. For the probe of the reaction products liquid beam desorption mass spectrometry was employed. A decisive feature of the technique is that ionic species, as well as neutral products and intermediates may be detected (neutrals as protonated aggregates) via time-of-flight mass spectrometry without any additional ionization laser. After the explosive disintegration of the superheated beam, high-temperature water reactions are efficiently quenched via expansion and evaporative cooling. For first exploratory experiments for chemistry in ultrahigh-temperature, -pressure and -density water, we have chosen resorcinol as a benchmark system, simple enough and well studied in high-temperature water environments much below 1000 K. Contrary to oxidation reactions usually present under less extreme and dense supercritical conditions, we have observed hydration and little H-atom abstraction during the narrow time window of the experiment. Small amounts of radicals but no ionic intermediates other than simple proton adducts were detected. The experimental findings are discussed in terms of the energetic and dense environment and the small time window for reaction, and they provide firm evidence for additional thermal reaction channels in extreme molecular environments.

Ultrafast electronic spectroscopy for chemical analysis near liquid water interfaces: concepts and applications

“…Nevertheless, the degree of understanding is often not sufficient. Water at extreme temperature and pressure conditions is surprisingly also a field of continuous strong interest [55][56][57]. Its hydrogen bond structure has been investigated theoretically and experimentally [58].…”

“…As in [1] the internal energies of the excited water phase have been estimated from the known absorption coefficients of water [57] and determined to be ≈10 and ≈40 kJ/mol corresponding to transient temperatures of ≈400 and ≈800 K, respectively. While the first traces of Fig.…”

Hydrogen bond dynamics of superheated water and methanol by ultrafast IR-pump and EUV-photoelectron probe spectroscopy

“…The pulse profile in the laser focus has been measured precisely with a knife-edge technique. 8 The fraction of the pulse energy hitting the liquid jet was determined from the jet diameter (B15-20 mm), the focus diameter and the intensity distribution of the IR-laser pulse (Fig. 2a).…”

“…17 Since the unique properties of SCW and SCM as solvents 4,5 in chemical reactions arise from fluctuations in the hydrogen bonding state and density (aggregate formation), information on their structures and dynamic properties is highly desired for understanding of the underlying mechanisms of chemical reactions and further development of supercritical fluids technology. [6][7][8] In this context, it is crucial to know to what extent H bonds persist in these fluids. 18 For water, this issue has already been addressed by neutron diffraction studies 19,20 using the isotopic substitution technique.…”

IR-MALDI ion mobility spectrometry

“…By means of the IR laser pulse, the irradiated volume was shown to be transferred into a supercritical state, which is characterized by extreme temperature and pressure conditions (1750 K, 30 kbar) in a time period of 20 to 30 ns [17]. As a result of the ensuing phase explosion, the liquid is dispersed into nano and micro droplets.…”