Detection Of Molecular Hydrogen Research Articles

Detection of dissolved hydrogen in water using platinum-modified boron doped diamond electrodes

The detection of molecular hydrogen in water using platinum modified boron doped diamond (Pt-BDD) was presented. A clear peak of hydrogen desorption was observed around −0.1 V in 0.1 M KCl solution. With a simple electrochemical pretreatment, the signal at Pt-BDD electrode was found to be higher and more stable compared to those using bare Pt electrode. The performance of the sensor was compared with gas chromatography method. The result shows a similar trend with either same or different concentration of H2. Lastly, the measurement was successfully conducted in the tap water even without addition of electrolyte. These result shows that Pt-BDD could be promoted as a good electrode candidate for sensing dissolved H2 in the water-based solution.

State Resolved Data for Quadrupole Radiative Association of H+H and Dissociation of H2 through Orbiting Resonances

Abstract We propose a reassessment of quadrupole radiative association and dissociation for the formation, destruction, and detection of molecular hydrogen in the early universe and in very cold molecular clouds by taking into account orbiting (shape) resonances. We provide accurate data needed for the modeling of this mechanism—namely, the energies and lifetimes of all the orbiting resonances up to J = 30 in the ground electronic state ( ) and the energies and quadrupole matrix elements for all the associated resonance–resonance and resonance-bound rovibrational transitions.

HST /COS SPECTRA OF DF Tau AND V4046 Sgr: FIRST DETECTION OF MOLECULAR HYDROGEN ABSORPTION AGAINST THE Lyα EMISSION LINE

We report the first detection of molecular hydrogen (H$_{2}$) absorption in the Lyman-$\alpha$ emission line profiles of two classical T Tauri stars (CTTSs), DF Tau and V4046 Sgr, observed by \emph{HST}/COS. This absorption is the energy source for many of the Lyman-band H$_{2}$ fluorescent lines commonly seen in the far-ultraviolet spectra of CTTSs. We find that the absorbed energy in the H$_{2}$ pumping transitions from a portion of the Lyman-$\alpha$ line significantly differ from the amount of energy in the resulting fluorescent emission. By assuming additional absorption in the H I Lyman-$\alpha$ profile along our light of sight, we can correct the H$_{2}$ absorption/emission ratios so that they are close to unity. The required H I absorption for DF Tau is at a velocity close to the radial velocity of the star, consistent with H I absorption in the edge-on disk and interstellar medium. For V4046 Sgr, a nearly face-on system, the required absorption is between +100 km/s and +290 km/s, most likely resulting from H I gas in the accretion columns falling onto the star.

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry

High-pressure methods have been demonstrated to be efficient in providing new routes for the synthesis of materials of technological interest. In several molecular compounds, the drastic pressure conditions required for spontaneous transformations have been lowered to the kilobar range by photoactivation of the reactions. At these pressures, the syntheses are accessible to large-volume applications and are of interest to bioscience, space, and environmental chemistry. Here, we show that the short-lived hydroxyl radicals, produced in the photodissociation of water molecules by near-UV radiation at room temperature and pressures of a few tenths of a gigapascal (GPa), can be successfully used to trigger chemical reactions in mixtures of water with carbon monoxide or nitrogen. The detection of molecular hydrogen among the reaction products is of particular relevance. Besides the implications in fundamental chemistry, the mild pressure and irradiation conditions, the efficiency of the process, and the nature of the reactant and product molecules suggest applications in synthesis.

Excitation mechanisms in newly discovered H2-bearing damped Lyman-αclouds: systems with low molecular fractions

Aims. We probe the physical conditions in high-redshift damped Lyman-α systems (DLAs) using the observed molecular fraction and the rotational excitation of molecular hydrogen. Methods. We search for Lyman- and Werner-band absorption lines of molecular hydrogen in the VLT/UVES spectra of background QSOs at the redshift of known DLAs. Results. We report two new detections of molecular hydrogen in the systems at zabs = 2.402 and 1.989 toward, respectively, HE 0027−1836 and HE 2318−1107, discovered in the course of the Hamburg-ESO DLA survey. We also present a detailed analysis of our recent H2 detection toward Q 2343+125. All three systems have low molecular fractions, log f ≤− 4, with f = 2N(H2)/(2N(H2) + N(H i)). Only one such H2 system was known previously. Two of them (toward Q 2343+125 and HE 2318−1107) have high-metallicities, [X/H] > −1, whereas the DLA toward HE 0027−1836 is the system with the lowest metallicity ([Zn/H] = −1.63) among known H2-bearing DLAs. The depletion patterns for Si, S, Ti, Cr, Mn, Fe and Ni in the three systems are found to be very similar to what is observed in diffuse gas of the Galactic halo. Molecular hydrogen absorption from rotational levels up to J = 5 is observed in a single well-defined component toward HE 0027−1836. We show that the width (Doppler parameter) of the H2 lines increases with increasing J and that the kinetic energy derived from the Doppler parameter is linearly dependent on the relative energy of the rotational levels. There is however no velocity shift between lines from different rotational levels. The excitation temperature is found to be 90 K for J = 0t oJ = 2a nd∼500 K for higher J levels. Single isothermal PDR models fail to reproduce the observed rotational excitations. A two-component model is needed: one component of low density (∼50 cm −3 ) with weak illumination (χ = 1) to explain the J ≤ 2 rotational levels and another of high density (∼500 cm −3 ) with strong illumination (χ = 30) for J ≥ 3 levels. However, the juxtaposition of these two PDR components may be ad-hoc and the multicomponent structure could result either from turbulent dissipation or C-shocks.

Metallicity as a criterion to select H2-bearing damped Lyman-$\mathsf{\alpha}$ systems

Aims. We characterize the importance of metallicity on the presence of molecular hydrogen in damped Lyman-α (DLA) systems. Methods. We constructed a representative sample of 18 DLA/sub-DLA systems with log N(H i) > 19.5 at high redshift (zabs > 1.8) and with metallicities relative to solar [X/H] > −1.3 (with [X/H] = log N(X)/N(H)−log (X/H)� and X either Zn, S or Si). We gathered data covering the expected wavelength range of redshifted H2 absorption lines on all systems in the sample from either the literature (10 DLAs), the UVES-archive, or new VLT-UVES observations for four of them. The sample is large enough to allow us to discuss for the first time the importance of metallicity as a criterion for the presence of molecular hydrogen in the neutral phase at high-z. Results. From the new observations, we report two new detections of molecular hydrogen in the systems at zabs = 2.431 toward Q 2343+125 and at zabs = 2.426 toward Q 2348−011. Q 2348−011, From a comparison of the H2 detection fraction in the highmetallicity sample with earlier results, we find that the fraction of DLA systems with log f = log 2N(H2)/(2N(H2) + N(H i)) > − 4i s as large as 50% for [X/H] > −0.7, when it is only ∼5% for [X/H] < −1.3 and ∼15% in the overall sample (with −2.5 < [X/H] < −0.3). This demonstrates that the presence of molecular hydrogen at high redshift is strongly correlated with metallicity.

The VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-$\alpha$ systems

We have searched for molecular hydrogen in damped Lyman-alpha (DLA) and sub-DLA systems at z>1.8 using UVES at the VLT. Out of the 33 systems in our sample, 8 have firm and 2 have tentative detections of associated H2 absorption lines. Considering that 3 detections were already known from past searches, H2 is detected in 13 to 20 percent of the newly-surveyed systems. We report new detections of molecular hydrogen at z=2.087 and 2.595 toward, respectively, Q 1444+014 and Q 0405-443, and also reanalyse the system at z=3.025 toward Q 0347-383. We find that there is a correlation between metallicity and depletion factor in both our sample and also the global population of DLA systems (60 systems in total). The DLA and sub-DLA systems where H2 is detected are usually amongst those having the highest metallicities and the largest depletion factors. Moreover, the individual components where H2 is detected have depletion factors systematically larger than other components in the profiles. In two different systems, one of the H2-detected components even has [Zn/Fe]>=1.4. These are the largest depletion factors ever seen in DLA systems. All this clearly demonstrates the presence of dust in a large fraction of the DLA systems. The mean H2 molecular fraction is generally small in DLA systems and similar to what is observed in the Magellanic Clouds. From 58 to 75 percent of the DLA systems have log f 1000 K) and/or the ionizing flux is enhanced relative to what is observed in our Galaxy.

Cosmological evolution of heavy-element andH2abundances

Spectroscopic observations of distant quasars have resulted in the detection of molecular hydrogen in intervening damped Lyman α absorption clouds (DLAs). We use observations compiled from different experimental groups to show that the molecular hydrogen abundance exhibits a dramatic increase over a cosmological time period corresponding to 13 to 24 per cent of the age of the Universe. We also tentatively show that the heavy-element abundances in the same gas clouds exhibit a faster and more well-defined cosmological evolution compared with the general DLA population over the same time baseline. We argue that this latter point is unsurprising, because the general DLA population arises in a wide variety of galaxy types and environments, and thus a spans broad range of ISM gas-phases and abundances at the same cosmic time. DLAs exhibiting H2 absorption may therefore circumvent this problem, efficiently identifying a narrower class of objects, and provide a more sensitive probe of cosmological chemical evolution.

The Very Large Telescope Ultraviolet and Visible Echelle Spectrograph survey for molecular hydrogen in high-redshift damped Lyman systems

We have searched for molecular hydrogen in damped Lyman α (DLA) and sub-DLA systems at high redshift (z abs > 1.8) using the Ultraviolet and Visible Echelle Spectrograph (UVES) at the Very Large Telescope (VLT) down to a detection limit of typically N(H 2 ) = 2 × 10 14 cm -2 . Out of the 33 systems in our sample, eight have firm and two have tentative detections of associated H 2 absorption lines. Considering that three detections were already known from past searches, molecular hydrogen is detected in 13-20 per cent of the newly surveyed systems. We report new detections of molecular hydrogen at z abs = 2.087 and 2.595 toward, respectively, Q 1444+014 and Q 0405-443, and also reanalyse the system at z abs = 3.025 toward Q 0347-383. In all of the systems, we measure metallicities relative to solar, [X/H] (with either X = Zn, S or Si), and depletion factors of Fe, [X/Fe], supposedly on to dust grains, and compare the characteristics of our sample with those of the global population of DLA systems (60 systems in total). We find that there is a correlation between the metallicity and the depletion factor in both our sample and also the global population of DLA systems. Although H 2 molecules are detected in systems with [Zn/Fe] as small as 0.3, the DLA and sub-DLA systems where H 2 is detected are usually amongst those having the highest metallicities and the largest depletion factors. In particular, H 2 is detected in the five systems having the largest depletion factors. Moreover, the individual components where H 2 is detected have depletion factors systematically larger than other components in the profiles. In two different systems, one of the H 2 -detected components even has [Zn/Fe]≥1.4. These are the largest depletion factors ever seen in DLA systems. All of this clearly demonstrates the presence of dust in a large fraction of the DLA systems. The mean H 2 molecular fraction, f= 2N (H 2 )/[2N(H 2 ) +N(H i)], is generally small in DLA systems (typically log f 2 and the H i column density. In fact, two systems where H 2 is detected have log N(H i) 2 on to dust grains is reduced in those systems, probably because the gas is warm (T > 1000 Κ) and/or the ionizing flux is enhanced relative to what is observed in our Galaxy.

Detection of molecular hydrogen atz = 1.15 toward HE 0515–4414

A new molecular hydrogen cloud is found in the sub-damped Lyα absorber [ () = ] at the redshift zabs = 1.15 toward the bright quasar HE 0515–4414 (zem = 1.71). More than 30 absorption features in the Lyman band system of H2 are identified in the UV spectrum of this quasar obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. The H2-bearing cloud shows a total H2 column density N(H2) cm-2 and a fractional molecular abundance derived from the H2 lines arising from the rotational levels of the ground electronic vibrational state. The estimated rate of photodissociation at the cloud edge s-1 is much higher than the mean Galactic disk value, s-1. This may indicate an enhanced star-formation activity in the system as compared with molecular clouds at where . We also find a tentative evidence that the formation rate coefficient of H2 upon grain surfaces at is a factor of 10 larger than a canonical Milky Way value, cm3 s-1. The relative dust-to-gas ratio estimated from the [Cr/Zn] ratio is equal to (in units of the mean Galactic disk value), which is in good agreement with a high molecular fraction in this system. The estimated line-of-sight size of pc may imply that the H2 is confined within small and dense filaments embedded in a more rarefied gas giving rise to the sub-damped Lyα absorber.

Detection of molecular hydrogen in a near Solar-metallicity damped Lyman-α system at $z_\mathsf{abs}$ ≈ 2 toward Q 0551-366

We report the detection of H_2, CI, CI*, CI** and Cl I lines in a near Solar-metallicity ([Zn/H]=-0.13) damped Lyman-alpha (DLA) system at z_abs=1.962 observed on the line of sight to the quasar Q 0551-366. The iron-peak elements, X=Fe, Cr and Mn are depleted compared to zinc, [X/Zn] -0.8, probably because they are tied up onto dust grains. Among the three detected H_2-bearing clouds, spanning 55 km s^-1 in velocity space, we derive a total molecular hydrogen column density N(H_2)=2.6x10^17 cm^-2 and a mean molecular fraction f=2N(H_2)/(2N(H_2)+N(HI))=1.7x10^-3. The depletion of heavy elements (S, Si, Mg, Mn, Cr, Fe, Ni and Ti) in the central component is similar to that observed in the diffuse neutral gas of the Galactic halo. This depletion is approximately the same in the six CI-detected components independently of the presence or absence of H_2. The gas clouds in which H_2 is detected always have large densities, n_H>30 cm^-3, and low temperatures, T_01<~100 K. This shows that presence of dust, high particle density and/or low temperature are required for molecules to be present. The photo-dissociation rate derived in the components where H_2 is detected suggests the existence of a local UV radiation field similar in strength to the one in the Galaxy. Star formation therefore probably occurs near these H_2-bearing clouds.

Far Ultraviolet Spectrum of Mars

A spectrum of Mars of unprecedented quality was obtained in the range of 904–1183 Å with a spectral resolution of 0.2 Å using the Far Ultraviolet Spectroscopic Explorer. Besides marking the first detection of molecular hydrogen on Mars (Krasnopolsky and Feldman, Science 2001 294, 1914–1917), the spectrum also revealed many emission lines of H, O, N, C, Ar, He, N +, C +, and Ar + and the bands of N 2 and CO. The spectrum makes it possible to study the emission multiplet structures and the component ratios and to separate many of the blended lines. From the argon lines, we retrieved Ar mixing ratios of 1.5 and 1.3% at 150 and 130 km, respectively, in excellent agreement with the Viking mass spectrometric measurements of 1.6% in the lower atmosphere. The He 584-Å emission observed in second order also agrees with the Extreme Ultraviolet Explorer detection of He on Mars. The observed spectrum may be used as a database to study specific problems such as the dayglow excitation, radiative transfer, and composition in Mars' upper atmosphere.

Detection of Molecular Hydrogen in the Atmosphere of Mars

Four hydrogen (H2) lines have been detected in a spectrum of Mars observed with the Far Ultraviolet Spectroscopic Explorer. Three of those lines are excited by the solar Lyman beta photons. The line intensities correspond to a column H2 abundance of 1.17 (+/-0.13) x 10(13) per square centimeter above 140 kilometers on Mars. A photochemical model for the upper atmosphere that simulates the observed H2 abundance results in an H2 mixing ratio of 15 +/- 5 parts per million in the lower atmosphere. The H2 and HD mixing ratios agree with photochemical fractionation of D (deuterium) between H2O and H2. Analysis of D fractionation among a few reservoirs of ice, water vapor, and molecular hydrogen on Mars implies that a global ocean more than 30 meters deep was lost since the end of hydrodynamic escape. Only 4% of the initially accreted water remained on the planet at the end of hydrodynamic escape, and initially Mars could have had even more water (as a proportion of mass) than Earth.

Detection of Molecular Hydrogen by Stimulated Raman Emission

Molecular hydrogen is a very difficult molecule to detect in a noninvasive manner. The molecule has no dipole moment. Excitation of its first electronic excited state requires light in the vacuum ultraviolet region, ~110 nm. Hydrogen has been shown to produce spontaneous Raman emission at pressures as low as 550 Torr, but the process occurs with a low quantum efficiency, and efficient collection of the emissions is difficult. Lower partial pressures of hydrogen can be detected with coherent anti-Stokes Raman spectroscopy (CARS), but the experimental apparatus can be prohibitively expensive.

Construction of a shuttered time-of-flight mass spectrometer for selective ion detection

By placing a pulsed, high-voltage steering plate between the ion source and detector in a time-of-flight mass spectrometer, the signal-to-noise ratio of the mass of interest is improved by more than an order of magnitude. This improvement arises from (1) suppression of ions of other masses formed at the same time as the ion of interest and (2) suppression of ions formed at different times and different locations whose arrival time at the detector is nearly coincident with the mass of interest. The advantages of this simple device are demonstrated in the detection of molecular hydrogen in the presence of other species.

Detection of molecular hydrogen in the Small Magellanic Cloud H II region N81

view Abstract Citations (23) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of molecular hydrogen in the Small Magellanic Cloud H II region N 81. Koornneef, J. ; Israel, F. P. Abstract Two micron near-infrared spectrophotometry of the compact H II region N81 in the Small Magellanic Cloud is presented. The resulting spectrum is similar to that of the bright galactic H II region G333.6-0.2. The paper reports the detection of molecular hydrogen emission, consistent with the presence of a mild shock moving into a dense ambient medium, which is due to the expansion of the H II region into an associated molecular cloud. Although the nebular core of N81 is virtually dust-free, a 3.76 microns excess suggests the presence of hot dust behind the visible nebula. N81 appears to be excited by a small cluster containing at least one early O star, and several late O and early B stars. Publication: The Astrophysical Journal Pub Date: April 1985 DOI: 10.1086/163051 Bibcode: 1985ApJ...291..156K Keywords: H Ii Regions; Infrared Astronomy; Magellanic Clouds; Molecular Clouds; Nebulae; Cosmic Dust; Interstellar Extinction; Spectrophotometry; Astrophysics full text sources ADS | data products SIMBAD (3) NED (1)

Detection of molecular hydrogen in two merging galaxies

NGC6240 and Arp 220 (IC4553) are two of the most luminous IR galaxies known1,2. They are also both thought to be examples of galaxy–galaxy mergers. As part of our study of interacting and merging galaxies1,3,4 we have obtained IR spectra in the 2-µm region of NGC6240 and Arp 220 and detected the ν = 1–0 S(1) quadrupole rotation–vibration emission line of H2 (rest wavelength 2.122 µm) in both galaxies. (This line in NGC6240 has also recently been detected by E. E. Becklin et al., personal communication.) These detections, which double the number of previously published measurements of extragalactic H2 (refs 5, 6) suggest that the merger of two galaxies results in the production of massive quantities of shocked molecular gas. This shocked gas must cool and collapse, leading to an enormous burst of star formation. These measurements of shocked H2 thus strengthen our earlier interpretation1 of the extremely large IR luminosity of NGC6240 in terms of a ‘super-starburst’. Arp 220 may be undergoing similar activity. We suggest that merging galaxies are a unique new class of ultra-luminous IR galaxies.

Quantum-State-Specific Detection of Molecular Hydrogen by Three-Photon Ionization

A sensitive method is demonstrated for determining (${v}^{\ensuremath{'}\ensuremath{'}}, {J}^{\ensuremath{'}\ensuremath{'}}$) populations of ${\mathrm{H}}_{2}$. Single rotational levels of the $E$, $F{^{1}\ensuremath{\Sigma}_{g}}^{+}$ state are prepared by two-photon excitation; absorption of a third quantum causes ionization. Detection of ${J}^{\ensuremath{'}\ensuremath{'}}$ levels of ${v}^{\ensuremath{'}\ensuremath{'}}=0, 1, \mathrm{and} 2$ is possible while scanning the dye laser fundamental over just 5 nm. Measured rotational populations at different temperatures (295-750 K) agree well with the corresponding Boltzmann distributions. Rotational line strengths show almost no ${J}^{\ensuremath{'}\ensuremath{'}}$ dependence for this process.