Spectra Of H2 Research Articles

Indication of a Cosmological Variation of the Proton-Electron Mass Ratio Based on Laboratory Measurement and Reanalysis ofH2Spectra

Based on highly accurate laboratory measurements of Lyman bands of H2 and an updated representation of the structure of the ground X 1sigma(g)+ and excited B 1sigma(u)+ and C 1pi(u) states, a new set of sensitivity coefficients K(i) is derived for all lines in the H2 spectrum, representing the dependence of their transition wavelengths on a possible variation of the proton-electron mass ratio mu = m(p)/m(e). Included are local perturbation effects between B and C levels and adiabatic corrections. The new wavelengths and K(i) factors are used to compare with a recent set of highly accurate H2 spectral lines observed in the Q 0347-383 and Q 0405-443 quasars, yielding a fractional change in the mass ratio of deltamu/mu = (2.4 +/- 0.6) x 10(-5) for a weighted fit and deltamu/mu = (2.0 +/- 0.6) x 10(-5) for an unweighted fit. This result indicates, at a 3.5sigma confidence level, that mu could have decreased in the past 12 Gyr.

High-order harmonic generation of hydrogen molecule irradiated by ultra-strong femto-second laser pulse——a simulation via TDDFT

The high order harmonic generation (HHG) of hydrogen molecule irradiated by ultra-strong femto-second laser pulse is simulated by the TTDFT method with the classical and quantum combination technique. The results indicate that the HHG spectra of H2 have a “decrease-plateau-cutoff” structure. A kind of “odd allowed, even forbidden” selective phenomenon of the order number of HHG is observed. Change in polarization direction of laser beam may change the cut-off order and spectrum intensity of HHG simultaneously.

Kinematic Structure of H2and [Feii] in the Bipolar Planetary Nebula M2-9

We present new high-dispersion, long-slit, infrared (IR) spectra of the double-shell bipolar planetary nebula M2-9 in the emission lines [Fe II] λ16435 and H2 v = 1–0 S(1) λ21218. H2 spectra reveal for the first time the kinematic structure of the shell in M2-9. Kinematics of the inner shell, traced by [Fe II], resemble those of optical forbidden lines like [N II] λ6583, although we note subtle differences. [Fe II] and H2 shells have expansion speeds roughly proportional to distance from the star (Hubble flows) and share the same dynamical age of 1200–2000 yr, depending on the distance to M2-9. Thus, the inner ionized lobes and molecular lobes, as well as the molecular torus and outer loops measured by other observers, were all formed around the same time. Consequently, their nested structure likely arises from an excitation gradient rather than independent ejections. H2 and [Fe II] emission is distributed more uniformly than [N II], and IR lines are not dominated by the moving ionization pattern like visual-wavelength lines. We suggest that this is because IR lines of [Fe II] and H2 are excited by relatively isotropic far-UV radiation (Balmer continuum), whereas optical lines respond to a directed rotating beam of Lyman continuum. Finally, we highlight intriguing similarities between M2-9 and the Homunculus of η Car, despite the different central engines powering the two nebulae.

Characterization of a radio frequency carbon nanotube growth plasma by ultraviolet absorption and optical emission spectroscopy

Radio frequency driven methane/hydrogen plasmas for carbon nanotube growth at pressures between 0.5 and 20Torr, bias power from 0to110W, and inductive coil power from 0to200W are characterized via optical diagnostics. Ultraviolet absorption spectroscopy is used for quantitative determination of CH3 radical density for these systems, giving densities on the order of 1013cm−3, accounting for approximately 0.1% of the plasma neutral content. Emission data are also analyzed to extract neutral gas temperatures from the H2 spectrum and electron densities and temperatures and approximate atomic H densities in the system. Neutral temperature is estimated between 700 and 1100K, though the lower electrode is heated to 1273K. Electron temperature is estimated to be between 2.5 and 3.5eV in the high-energy (>12eV) portion of the electron energy distribution, and the data suggest an overall non-Maxwellian distribution of electrons. The dissociation of hydrogen is estimated at around 0.1%. Dependencies on power and pressure are explored, indicating more efficient ionization, dissociation, and electron heating at lower pressure and higher power. The absence of any dependency on coil power suggests the plasma is operating in a noninductive mode for these conditions.

High resolution infrared spectra of H2–Kr and D2–Kr van der Waals complexes

Infrared spectra of weakly bound hydrogen-krypton complexes have been studied at high spectral resolution (0.04 cm(-1)) using a long-path (154 m) low temperature (100 K) absorption cell and a Fourier transform spectrometer. In addition to spectra from the regions of the H(2) and D(2) fundamental vibrational bands in the midinfrared, the results also include the region of the pure rotational S(0)(0) transition of H(2) in the far infrared. A total of 219 measured line positions from these spectra have been fully assigned to specific quantum transitions and form the basis for determining a greatly improved semiempirical three-dimensional intermolecular potential energy surface for hydrogen-krypton in an accompanying paper.

The threshold electron impact spectrum of H2O

The threshold electron spectrum of H2 O was obtained using a high resolution electron impact spectrometer combined with the penetrating field method for scattered electrons with energies close to zero eV. The valence, triplet Rydberg states, as well as the resonances were identified and are discussed in the energy region 5.2–14.3 eV. The threshold spectrum confirms the influence of resonances on the enhancement of the intensity of some Rydberg states above 10 eV. The vibrational spacing of the observed transitions of the Rydberg states indicates that the water molecule is excited in the symmetric stretching mode.

Isotope effects for molecules in a cavity

A model problem of the motion of a particle in an impenetrable cavity is considered in order to establish how the energy levels and transition energies between them depend on the linear size, R, of the cavity and on the particle mass. In the case of one particle problem with a uniform potential inside the cavity there exists a simple qualitative solution that describes the effect of the cavity size and shows that a decrease in R can cause the isotopic frequency shift to increase as compared to the free system. The estimates obtained were used to interpret the results of numerical calculations of low lying energy states of hydrogen molecule and its isotopomers confined within impenetrable spherical cavity. The effect of the cavity radius on the structure of the low lying part of the energy spectra of H2, D2, and HD molecules and on the reliability of adiabatic separation of nuclear variables are considered. The approach provides a qualitatively correct description of the changes in the energy level positions but the behavior of the isotopic frequency ratio is too smooth compared with results of more accurate calculations.

Unusual Forms of Molecular Hydrogen Adsorption by Cu+1 Ions in the Copper-Modified ZSM-5 Zeolite

DRIFT and IR transmittance spectra of H2 adsorbed at 77 K or at room temperature by the copper-modified ZSM-5 zeolite pre-evacuated or pre-reduced in CO at 873 K indicated several unusual forms of adsorbed hydrogen. H–H stretching frequencies of adsorbed species at 3075–3300 cm−1 are by about 1000 cm −1 lower than in the free hydrogen molecules. This indicates unusually strong perturbation of adsorbed hydrogen by reduced Cu +1 ions that has been never before reported neither for hydrogen nor for adsorption of other molecules by any cationic form of zeolites or oxides.

The dynamics of H2 and N2 sorption in carbon nanotubes

Single-walled and multi-walled carbon nanotubes (SWNT and MWNT) were prepared by catalytic decomposition of methane and acetylene, respectively. The resulting catalyst/carbon composites were subjected to chemical treatments to obtain samples which were enriched in nanotubes. Isotherms and frequency response (FR) spectra of N2 and H2 were recorded at 195 and 77K, respectively, in the 1–800Pa pressure range. The adsorption isotherms for N2 were found to obey Henry’s law, while the isotherms of H2 adsorption indicated some energetic heterogeneity of the sorption sites. Stronger adatom–substrate interaction was detected for those samples which had been subjected to oxidative treatment. The FR measurements showed that treatment of MWNT in KMnO4 solution changed the rate-controlling mechanism of mass transport from one of sorption to one of diffusion. Results substantiated that the surface functional groups, generated by the oxidative treatment, have significant influence on both the equilibrium and the dynamic N2 and H2 sorption properties of the carbon nanotubes.

Measurement and simulation of spontaneous Raman scattering in high-pressure fuel-richH2–air flames

Rotational and vibrational spontaneous Raman scattering (SRS) spectra ofH2,N2 andH2O have beenmeasured in H2–air flames at pressures up to 30.4 bar as a first step towards establishing a comprehensiveRaman spectral database for temperatures and species in high-pressure combustion. Wehave obtained an initial set of measurements that indicate the spectra are of sufficientquality in terms of spectral resolution, wavelength coverage and signal-to-noise ratio for usein the development of transferable standards for the cross-talk calibration matrix.The fully resolved Stokes and anti-Stokes shifted spectra were collected in thevisible wavelength range (400–700 nm) using pulse-stretched 532 nm excitationand a spectrograph fitted with a non-intensified CCD detector and a high-speedshutter. Temperatures were determined via the intensity distribution of rotationalH2 lines at stoichiometric and fuel-rich conditions. A discussion of the temperaturemeasurement accuracy in terms of the number of laser shots, including a single-shotmeasurement, is presented. Theoretical Raman spectra of hydrogen were calculated using asemi-classical anharmonic-oscillator model with recent pressure broadening dataand were compared with experimental data. The data and simulation showedgood agreement at different equivalence ratios and pressures and indicate thathigh-J rotationallines of H2 mayinterfere with the N2 vibrational Q-branch lines, which could lead to errors inN2-Raman thermometry based on the line-fitting method. In addition, the relative intensities of theO- andS-branchesto the Q-branch were determined theoretically and the result indicates thatfurther studies of spectral interferences including contributions fromO- andS-branches should be pursued. Finally, from a comparison ofN2 Q-branchspectra in lean H2–air flames at nearly atmospheric (1.2 bar) and high pressure (30.4 bar), we found nosignificant line-narrowing or -broadening effects at a spectral resolution of 0.04 nm.

Doubly Excited Molecules in Electron Collisions as Studied by Coincident Electron-Energy-Loss Spectroscopy

Electron energy-loss spectra of H2, D2 and N2 tagged with emissive neutral-dissociation, i.e. coincident electron-energy-loss spectra, were measured in the range where doubly excited states of these molecules lie. The doubly excited states, in particular forbidden ones with dissociative character, were revealed for the first time in electron-molecule collisions. It has turned out that this method, the coincident electron-energy-loss spectroscopy, is a key tool for investigating doubly excited molecules.

Variational calculations of excited states with zero total angular momentum (vibrational spectrum) of H2 without use of the Born–Oppenheimer approximation

Very accurate, rigorous and fully variational, all-particle, non-Born–Oppenheimer calculations of the vibrational spectrum of the H2 molecule have been performed. Very high accuracy has been achieved by expanding the wave functions in terms of explicitly correlated Gaussian functions with preexponential powers of the internuclear distance. An indicator of the high accuracy of the calculations is the new upper bound for the H2 nonrelativistic nonadiabatic ground state energy equal to −1.164 025 030 0 hartree.

Flux‐Velocity Relation for H2Outflows

We present an analysis of velocity-resolved near-IR molecular hydrogen observations of a variety of protostellar outflows with very different energetics, degrees of collimation, and morphologies. Observations in the 2.12 μm line of H2 were obtained using an IR Fabry-Pérot interferometer with a spectral resolution of 23 km s-1. The integrated flux-velocity diagrams for each outflow show a flat spectrum for low velocities followed by a decreasing power law dF/dv ∝ vγ, with γ between -1.8 and -2.6, for velocities higher than a clearly defined break velocity at 2-17 km s-1. Contrary to shock model predictions, it is shown that the H2 intensity is constant with velocity. We argue that the flux-velocity relation can then be interpreted as a mass-velocity relation, in striking similarity to the power-law mass spectra observed in CO outflows. By comparing H2 and CO mass-velocity spectra, it is shown that there is a velocity regime in which both molecules coexist and produce similar γ-values. Evolution effects in outflows appear as a correlation between outflow length and γ; as outflows age, the spectra becomes steeper. Our results support a common physical origin for both CO and H2 emission and a strong association between the molecular outflows traced in each molecule.

A new constraint on cosmological variability of the proton-to-electron mass ratio

Exotic cosmologies predict the variability of the fundamental physical constants over the cosmic time. Using the Very Large Telescope/Ultraviolet-Visual Echelle Spectrograph (VLT/UVES) high-resolution spectra of the quasar Q0347–3819 and unblended electronic-vibrational-rotational lines of the H2 molecule identified at zabs=3.025 we test possible changes in the proton-to-electron mass ratio μ0=mp/me over the period of ∼11 Gyr. We obtained a new constraint on the time-averaged variation rate of μ0 of ∣μ̇/μ0∣<5×10-15 yr-1 (1σ confidence level). The estimated 1σ uncertainty interval of the ∣Δμ/μ0∣ ratio of about 0.004 per cent implies that since the time when the H2 spectrum was formed at zabs=3.025, μ0 has not changed by more than a few thousandths of a per cent.

Raman spectroscopic investigation of H2, HD, and D2 physisorption on ropes of single-walled, carbon nanotubes.

We have observed the S- and Q-branch Raman spectra of H2, HD, and D2 adsorbed at 85 K and pressures up to 8 atm on single-walled, carbon nanotubes (SWNT). Comparative data for H2 on graphite and C60 were also collected. Frequency-downshifted and upshifted features were observed in the Q-branch spectra of H2 on C60 and SWNT. These shifts are small and are therefore inconsistent with charge transfer. An H2-surface potential with van der Waals and electrostatic terms was developed and used to estimate the shifts in the frequency of the Q(0) transition of H2 adsorbed in two types of sites. These calculations corroborate the experimental findings and indicate physisorption in multiple sites of the SWNT ropes.

Key to understanding interstitial H2 in Si.

A new IR absorption line at 3191.1 cm(-1) has been discovered for the interstitial HD molecule in Si. This new line appears for sample temperatures above approximately 20 K and lies 73.9 cm(-1) below the 3265.0 cm(-1) line previously observed for HD. We attribute the 73.9 cm(-1) energy difference to the rotation of the interstitial HD molecule. The selection rules associated with these two lines are consistent with the puzzling absence of an ortho-para splitting in the IR absorption spectra of H2 and D2 in Si.

Rotationally resolved infrared spectroscopy of h2- and d1-formic acid monomer in liquid He droplets

Rotationally resolved spectra of h2- and d1-formic acid embedded in liquid helium droplets have been recorded in the spectral region of the O–H (ν1) and C–H (ν2) stretch vibrations. Accidental resonant mixing between the ν1-band of h2-formic acid and the combination bands (ν2+ν7) and (ν2+ν9) has been observed. The fundamental ν1 band can interact via Fermi resonance with the (ν2+ν7), and the (ν2+ν7) via Coriolis coupling with the (ν2+ν9) band. Examination of the resonance induced line-broadening effects suggests that the helium environment modifies vibrational relaxation dynamics. The 2ν3 C=O stretch overtone is also observed and was assigned by a density functional theory (DFT) ab initio calculation. The spectroscopic constants are determined by fitting all spectra with a standard gas phase Hamiltonian.

Time‐resolved Electron Impact Study of Excitation of H 2 Singlet‐ Gerade States from Cascade Emission in the Vacuum Ultraviolet Region

Medium-resolution (full width at half-maximum Δλ = 0.5 A) vacuum ultraviolet (VUV) emission spectra of H2 from forbidden excitation to the excited singlet-gerade states and subsequent cascade to the singlet-ungerade states have been studied with a time-resolved electron-impact technique. Emissions from the B 1Σ, C 1Πu, B' 1Σ, and D 1Πu states that are entirely due to cascade from the singlet-gerade states have been observed. Lyman band emission intensities dominate over the entire 940-1650 A wavelength region, though Werner band emission intensities are also significant. In addition, very weak cascade emissions from the vj = 0 and 1 levels of the B' 1Σ and D 1Πu states are also evident. In contrast to previous assumption, the cascade excitation is observed to take place over all the vibrational levels of the B 1Σ and C 1Πu states, while contributing heavily to low vj levels of the B 1Σ state. Synthetic spectra based on the calculated transition probabilities of the EF 1Σ, GK 1Σ, H 1Σ, I 1Πg, J 1Δg, O 1Σ and P 1ΣB 1Σ, C 1Πu, B' 1Σ, and D 1Πu band systems and Franck-Condon factors of the EF 1Σ-X 1Σ, GK 1Σ-X 1Σ, H 1Σ-X 1Σ, I 1Πg-X 1Σ, J 1Δg-X 1Σ, O 1Σ-X 1Σ, and P 1Σ-X 1Σ are in good agreement with the observed Lyman and Werner band intensities. The present study shows that a number of singlet-gerade and singlet-ungerade states are involved in the cascade excitation process of H2. The cascade from these states in the VUV provide diagnostic information on astrophysical sources for H2 emission.

Interaction of phycobilisomes with photosystem II dimers and photosystem I monomers and trimers in the cyanobacterium Spirulina platensis.

Distribution of phycobilisomes between photosystem I (PSI) and photosystem II (PSII) complexes in the cyanobacterium Spirulina platensis has been studied by analysis of the action spectra of H2 and O2 photoevolution and by analysis of the 77 K fluorescence excitation and emission spectra of the photosystems. PSI monomers and trimers were spectrally discriminated in the cell by the unique 760 nm low-temperature fluorescence, emitted by the trimers under reductive conditions. The phycobilisome-specific 625 nm peak was observed in the action spectra of both PSI and PSII, as well as in the 77 K fluorescence excitation spectra for chlorophyll emission at 695 nm (PSII), 730 nm (PSI monomers), and 760 nm (PSI trimers). The contributions of phycobilisomes to the absorption, action, and excitation spectra were derived from the in vivo absorption coefficients of phycobiliproteins and of chlorophyll. Analyzing the sum of PSI and PSII action spectra against the absorption spectrum and estimating the P700:P680 reaction center ratio of 5.7 in Spirulina, we calculated that PSII contained only 5% of the total chlorophyll, while PSI carried the greatest part, about 95%. Quantitative analysis of the obtained data showed that about 20% of phycobilisomes in Spirulina cells are bound to PSII, while 60% of phycobilisomes transfer the energy to PSI trimers, and the remaining 20% are associated with PSI monomers. A relevant model of organization of phycobilisomes and chlorophyll pigment-protein complexes in Spirulina is proposed. It is suggested that phycobilisomes are connected with PSII dimers, PSI trimers, and coupled PSI monomers.

H2Emission Spectra with New Formation Pumping Models

It has been predicted that H2 newly formed on the surface of dust grains should be in highly vibrationally and rotationally excited states in the ground electronic state via the formation pumping mechanism. This suggests that the rovibrational emission spectrum of H2 may be detectable even in regions without a source of UV pumping or dynamical excitation. Moreover, the infrared H2 emission arising from formation pumping can be a new probe that will directly show us the spot where the evolution from H I clouds to H2 clouds occurs. In the present work, we investigate the pure effects of formation pumping in infrared H2 emission spectra with our new formation pumping models. We build up our formation pumping models for H2 newly formed on icy mantles, carbonaceous dust, and silicate dust, on the basis of the recent progress of basic studies about the H2 formation process on the surface of dust grains. Then, we calculate the H2 emission spectra with our new formation pumping models, considering the early stage of an evolving region from H I clouds to H2 clouds dominated by the H2 formation process on the surface of dust grains, of uniform H I density nH = 103 cm-3 and the gas temperature T = 10 K, in the cold interior of interstellar clouds under a weak ultraviolet (UV) radiation field. We find that the resulting infrared H2 emission spectra dominated by formation pumping can be discriminated from those dominated by UV pumping as well as have information about the property of dust. We also find that the fluxes of the most intense emission lines arising from formation pumping should be strong enough to be detected. In the wavelength range λ 1.6 μm, if the line intensities of many transitions from higher rotational states such as 1-0 S(3), 1-0 S(5), and 1-0 S(7) become stronger than that of the 1-0 S(1) transition, it should be the evidence of H2 emission arising from formation pumping. In the wavelength range λ 1.6 μm, if many transitions from higher vibrational states are detected, the emission should be originated from H2 newly formed on icy mantles or silicate dust. On the contrary, if not, the emission should be from H2 formed on carbonaceous dust.