Ultraviolet Laser-induced Fluorescence Spectroscopy Research Articles

Organic Material Distribution in Mars-Analog Volcanic Rocks, as Determined with Ultraviolet Laser-Induced Fluorescence Spectroscopy.

Understanding the distribution of trace organic material in a rocky environment is a key to constraining the material requirements for sustaining microbial life. We used an ultraviolet laser-induced fluorescence (LIF) spectroscopy instrument to characterize the distribution of organic biosignatures in basalts collected from two Mars-analog environments. We correlated the fluorescence results with alteration-related sample properties. These samples exhibit a range of alteration conditions found in the volcanic environments of Hawai'i Volcanoes National Park, Hawai'i (HI), and Craters of the Moon National Monument, Idaho (ID), including fumarolic systems. LIF mapping of the sample surfaces and interiors showed a heterogeneous distribution of areas of highly fluorescent material (point[s]-of-interest [POIs])-with fluorescence characteristics indicative of organic material. Results suggest that POIs are associated with secondary alteration mineral deposits in the rock's vesicles, including zeolites and calcite. Scanning electron microscopy with electron-dispersive X-ray spectroscopy was used to characterize the mineralogy present at POIs and support the evidence of carbon-bearing material. Overall, samples collected proximate to active or relict meteoric fumaroles from Hawai'i were shown to contain evidence for organic deposits. This suggests that these minerals are measurable spectroscopic targets that may be used to inform sample-site selection for astrobiology research.

Kinetics and Mechanism of Chlorine-Atom-Initiated Oxidation of Allyl Alcohol, 3-Buten-2-ol, and 2-Methyl-3-buten-2-ol

The gas-phase reactions of Cl atoms with allyl alcohol (k(1)), 3-buten-2-ol (k(2)), and 2-methyl-3-buten-2-ol (k(3)) at 296 +/- 2 K have been investigated using absolute and relative rate methods in 1-700 Torr of N(2) diluent. Absolute rate studies were performed using pulsed laser photolysis/vacuum ultraviolet laser-induced fluorescence spectroscopy techniques. Relative rate studies were performed using smog chamber/Fourier transform infrared spectroscopy techniques. The absolute and relative rate studies gave consistent results. The kinetics of the reactions are dependent on pressure over the range studied. Molar yields for HCl production in 700 Torr of N(2) for reactions of chlorine atoms with allyl alcohol, 3-buten-2-ol, and 2-methyl-3-buten-2-ol were measured to be 0.26 +/- 0.03, 0.23 +/- 0.03, and 0.12 +/- 0.02, respectively. The chlorine-atom-initiated oxidation of 2-methyl-3-buten-2-ol in 700 Torr of air gave the following products (molar yields): acetone (47 +/- 4%), chloroacetaldehyde (47 +/- 5%), and HCHO (7.2 +/- 0.6%). The observation of substantial and indistinguishable yields of acetone and chloroacetaldehyde products indicates that a major fraction of the reaction proceeds via addition of chlorine atoms to the terminal carbon atom. The results are discussed with respect to the literature data.

Rate constants of the O( 1D) reactions with N 2, O 2, N 2O, and H 2O at 295 K

Using a technique of laser flash photolysis coupled with vacuum ultraviolet laser-induced fluorescence spectroscopy, the rate coefficients of O( 1D) reactions with N 2, O 2, N 2O, and H 2O at 295 ± 2 K have been determined to be k N 2 = ( 3 . 29 ± 0 . 27 ) × 10 - 11 , k O 2 = ( 4 . 06 ± 0 . 24 ) × 10 - 11 , k N 2 O = ( 1 . 35 ± 0 . 08 ) × 10 - 10 and k H 2 O = ( 2 . 07 ± 0 . 18 ) × 10 - 10 cm 3 molecule - 1 s - 1 . The quoted uncertainties include estimated errors and are the 95% confidence level. The k N 2 and k N 2 O values obtained are larger than the current NASA/JPL recommendations by 26% and 16%, respectively, although they are still within the error limits associated with the recommendations.

Laser-induced fluorescence study of the quenching of Cl( 2P 1/2) in collisions with N 2 molecules and rare gas atoms

The rate constants of physical quenching of Cl( 2P 1/2) in collisions with N 2 molecules and rare gas atoms (Rg = He, Ne and Ar) at 295 ± 2 K were investigated using a technique of vacuum ultraviolet laser-induced fluorescence spectroscopy. The rate constants determined are (7.6 ± 0.8) × 10 −15, (5.7 ± 0.3) × 10 −14, ⩽8 × 10 −16 and ⩽5 × 10 −16 cm 3 molecule −1 s −1 for collision partners of N 2, He, Ne and Ar, respectively.

Quantum Yield for O(1D) Production from Ozone Photolysis in the Wavelength Range of 193−225 nm

The quantum yield values for O(1D) production from the photodissociation reaction of O3 between 193 and 225 nm at 298 ± 2 K are reported. The O(1D) photofragments have been detected directly using a technique of vacuum ultraviolet laser-induced fluorescence spectroscopy at 115.22 nm which is associated with the electronic transition of O(3s1D° − 2p1D). It has been found that the O(1D) quantum yield values decrease monotonically as the photolysis wavelength becomes shorter from 0.90 ± 0.12 (225 nm) to 0.48 ± 0.03 (193 nm). Photodissociation processes of O3 around 210 nm and its atmospheric implications have been discussed.

Determination of the heat of formation of O3 using vacuum ultraviolet laser-induced fluorescence spectroscopy and two-dimensional product imaging techniques

Two different techniques, vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy and two-dimensional (2D) ion counting product imaging, have been used to determine the bond energy for the dissociation of jet-cooled O3 into O(1D)+O2(a 1Δg). The photofragment excitation (PHOFEX) spectrum for O(1D) products is recorded by detecting the VUV-LIF signal associated with the 3s 1D0–2p 1D transition at 115.22 nm while scanning the photolysis laser wavelength between 305 and 313 nm. A clear cut-off corresponding to the appearance threshold into O(1D)+O2(a 1Δg) is observed in this PHOFEX spectrum. The 2D image of the O(1D) products from the O3 photolysis near 305 nm is measured using an ion-counting method, with the detection of O(1D) atoms by [2+1] resonance enhanced multiphoton ionization (REMPI) at 205.47 nm. The kinetic-energy distribution obtained from the 2D image shows rotational structure due to the O2(a 1Δg,v″=0) fragment. The bond energy into O(1D)+O2(a 1Δg) has been obtained from the rotational assignments in the kinetic-energy distribution. The two different experimental approaches give consistent results and an accurate value of the bond dissociation energy into O(1D)+O2(a 1Δg) is found to be 386.59±0.04 kJ/mol. The standard heat of formation of O3, ΔfH0(O3)=−144.31±0.14 kJ/mol, has also been calculated from the bond energy obtained, in conjunction with thermochemical data for O2 molecule and O atom. The uncertainty for the ΔfH0(O3) value obtained in the present study is smaller than the previous value which has been used widely.

Vacuum ultraviolet laser spectroscopy: Radiative lifetimes of interacting 2Δ states of NO

Interactions between the B′ 2Δ non-Rydberg state and nearby 2Δ Rydberg states of NO have been studied by vacuum ultraviolet laser-induced fluorescence spectroscopy. By using tunable, coherent radiation in the 60 000–70 000 cm−1 range, NO molecules in a supersonic jet were excited and their radiative decay was monitored by time-resolved fluorescence detection. In this way accurate, collision-free radiative lifetimes were measured for several levels of the B′ 2Δ, F 2Δ, N 2Δ, and D 2Σ+ excited states of NO. Using these lifetimes the oscillator strengths for the B′–X and F–X transitions were calculated. The radiative lifetimes for the perturbed states were quite different from the unperturbed lifetimes, and these changes are discussed in terms of the known interactions between states in this spectral region. For the unperturbed vibrational levels of the B′ 2Δ state, radiative lifetimes between 129–139 ns were measured, while for the F 2Δ state, a radiative lifetime of 30 ns was measured. For the perturbed bands of the F2Δ and B′ 2Δ states, the radiative lifetimes were accurately described by a two-state homogeneous perturbation model, but for the B′(v=7)∼N(v=0) mixed states, the lifetimes were dramatically different from those expected on the basis of two interacting states. This is caused by a third-interacting state whose identity is not known. The B′(v=8,9) states, while having unperturbed line positions, have shorter radiative lifetimes, indicating the onset of predissociation in those levels.