Oleksandr Sukhorukov

Pulsed quantum cascade laser-based cavity ring-down spectroscopy for ammonia detection in breath

Breath analysis can be a valuable, noninvasive tool for the clinical diagnosis of a number of pathological conditions. The detection of ammonia in exhaled breath is of particular interest for it has been linked to kidney malfunction and peptic ulcers. Pulsed cavity ringdown spectroscopy in the mid-IR region has developed into a sensitive analytical technique for trace gas analysis. A gas analyzer based on a pulsed mid-IR quantum cascade laser operating near 970 cm(-1) has been developed for the detection of ammonia levels in breath. We report a sensitivity of approximately 50 parts per billion with a 20 s time resolution for ammonia detection in breath with this system. The challenges and possible solutions for the quantification of ammonia in human breath by the described technique are discussed.

Kinetic Isotope Effects for the Reactions of Muonic Helium and Muonium with H2

Calculated reaction rates for two hydrogen isotopes, one 36 times heavier than the other, agree with experiments at 500 kelvin. The neutral muonic helium atom may be regarded as the heaviest isotope of the hydrogen atom, with a mass of ~4.1 atomic mass units (4.1H), because the negative muon almost perfectly screens one proton charge. We report the reaction rate of 4.1H with 1H2 to produce 4.1H1H + 1H at 295 to 500 kelvin. The experimental rate constants are compared with the predictions of accurate quantum-mechanical dynamics calculations carried out on an accurate Born-Huang potential energy surface and with previously measured rate constants of 0.11H (where 0.11H is shorthand for muonium). Kinetic isotope effects can be compared for the unprecedentedly large mass ratio of 36. The agreement with accurate quantum dynamics is quantitative at 500 kelvin, and variational transition-state theory is used to interpret the extremely low (large inverse) kinetic isotope effects in the 10−4 to 10−2 range.

Rotational spectroscopic study of hydrogen cyanide embedded in small 4He clusters

High resolution microwave spectra of the a-type, J = 1-0, transitions of He(N = 1-6)-H(12)C(14)N, He(N = 1-6)-H(13)C(14)N, He(N = 1-6)-H(12)C(15)N, He(N = 1-7)-D(12)C(14)N, and He(N = 1-6)-D(13)C(14)N clusters produced in a supersonic jet expansion were measured and analyzed. The resulting effective rotational constants, B(eff), initially decrease with the number of the attached helium atoms before reaching a minimum at N = 3 helium atoms for all isotopologues. The subsequent increase in B(eff) for N ≥ 4 is indicative of the onset of microscopic superfluidity. Comparison of our experimental B(eff) constants with those from quantum Monte Carlo simulations [A. A. Mikosz, J. A. Ramilowski, and D. Farrelly, J. Chem. Phys. 125, 014312 (2006)] reveals a nearly congruent trend in B(eff) for N up to 6. Analysis of the hyperfine structure of the (14)N containing isotopologues yielded a gradual incremental increase in the magnitude of χ(aa) and for N = 1-6, which suggests the internal rotation of the HCN molecule is becoming increasingly hindered.

Ultraviolet spectroscopy of pyrene in a supersonic jet and in liquid helium droplets

In a series of experiments devoted to the study of polycyclic aromatic hydrocarbons for astrophysical applications, the S(2)<--S(0) transition of jet-cooled pyrene (C(16)H(10)) at 321 nm has been studied by an absorption technique for the first time. The spectra observed by cavity ring-down spectroscopy closely resemble the excitation spectra obtained earlier by laser-induced fluorescence (LIF) and show the same band clusters arising from the vibronic interaction of S(2) with S(1). We have also investigated pyrene when it was incorporated into 380 mK cold helium droplets. These spectra which were recorded employing LIF and molecular beam depletion spectroscopy are broadened and redshifted by 0.94 nm but retain the essential features of the gas phase spectra.

Direct Spectroscopic Detection of the Orientation of Free OH Groups in Methyl Lactate–(Water)1,2 Clusters: Hydration of a Chiral Hydroxy Ester†

Hydration of chiral molecules is a subject of significant current interest in light of recent experimental observations of chirality transfer from chiral solutes to water in solution and the important roles which water plays in biological events. Using a broadband chirped pulse and a cavity based microwave spectrometer, we detected spectroscopic signatures of the mono- and dihydrates of methyl lactate, a chiral hydroxy ester. Surprisingly, these small hydration clusters show highly specific binding preferences. Not only do they strongly prefer the insertion H-bonding topology, but they also favor specific pointing direction(s) for their non-H-bonded hydroxy group(s). We observed that the particular dihydrate conformer identified is not the most stable one predicted. This work highlights the superior capability of high-resolution spectroscopy to identify specific water binding topologies, and provides quantitative data to test state-of-the-art theory.

Chirped‐Pulse and Cavity‐Based Fourier Transform Microwave Spectra of the Methyl Lactate⋅⋅⋅Ammonia Adduct

Author Institution: Department of Chemistry, University of Alberta, Edmonton, AB; T6G 2G2, Canada

Cavity ring-down spectroscopy with a pulsed distributed feedback quantum cascade laser

A pulsed distributed feedback quantum cascade laser operating near 970 cm-1 (10.3 μm) was coupled with the technique of cavity ring-down spectroscopy, as described here for the first time. The newly constructed set-up was tested by recording three relatively weak rotational lines of the 1000→0001 vibrational band of CO2 in the range from 966.75 cm-1 to 971.5 cm-1. The CO2 lines were recorded by measuring the decay time of a CO2 - N2 mixture flowing through an open sample tube placed between the cavity ring-down mirrors. The quantum cascade laser frequency was tuned at a rate of ~ 0.071 cm-1/K by changing the heat sink temperature in the range between -20 and 50 °C. The first results demonstrated the applicability and high sensitivity of the cavity ring-down spectroscopy - pulsed quantum cascade laser combination and encouraged us to extend our research to the study and detection of ammonia. We demonstrated that a detection limit of ammonia of ~ 25 ppbv can be attained with the current set-up. Basic instrument performance and optimization of the experimental parameters for sensitivity improvement are discussed.

First accurate experimental study of Mu reactivity from a state-selected reactant in the gas phase: the Mu + H2{1} reaction rate at 300 K

This paper reports on the experimental background and methodology leading to recent results on the first accurate measurement of the reaction rate of the muonium (Mu) atom from a state-selected reactant in the gas phase: the Mu + H2 MuH + H reaction at 300 K, and its comparison with rigorous quantum rate theory, Bakule et al (2012 J. Phys. Chem. Lett. 3 2755). Stimulated Raman pumping, induced by 532 nm light from the 2nd harmonic of a Nd:YAG laser, was used to produce H2 in its first vibrational (v = 1) state, H, in a single Raman/reaction cell. A pulsed muon beam (from ‘ISIS’, at 50 Hz) matched the 25 Hz repetition rate of the laser, allowing data taking in equal ‘Laser-On/Laser-Off’ modes of operation. The signal to noise was improved by over an order of magnitude in comparison with an earlier proof-of-principle experiment. The success of the present experiment also relied on optimizing the overlap of the laser profile with the extended stopping distribution of the muon beam at 50 bar H2 pressure, in which Monte Carlo simulations played a central role. The rate constant, found from the analysis of three separate measurements, which includes a correction for the loss of concentration due to collisional relaxation with unpumped H2 during the time of each measurement, is = 9.9[(−1.4)(+1.7)] × 10−13 cm3 s−1 at 300 K. This is in good to excellent agreement with rigorous quantum rate calculations on the complete configuration interaction/Born–Huang surface, as reported earlier by Bakule et al, and which are also briefly commented on herein.