Presence Of Buffer Gas Research Articles

Iron doped LiCoPO4 thin films for lithium-ion microbatteries obtained by ns pulsed laser deposition

Well crystallized and homogeneous iron doped LiCoPO4 (LCfP) thin films have been grown by ns Pulsed Laser Ablation, at ambient temperature without any substrate heating or post-annealing treatments. The films have been deposited in vacuum and in the presence of buffer gases (O2, Ar) and it has been found that their crystallinity, structure and morphology depend on pressure conditions. The films have been studied by Scanning Electron Microscopy and X Ray Diffraction, while their first steps of growth have been characterized by Transmission Electron Microscopy. A study of the plasma produced by the laser ablation in the different pressure conditions has been carried out with the aim of elucidate the mechanisms involved in the films deposition. LCfP thin films have been also tested as microelectrodes in lithium cells in galvanostatic condition for analyzing the reversibility of the lithium-ion battery.

Fourier-transform spectroscopy and description of low-lying energy levels in the B(1)1Π state of RbCs

The Fourier transform spectrometer with resolution of 0.03 cm(-1) was applied to disperse the diode laser induced B(1)(1)Π → X(1)Σ(+) fluorescence spectra of the RbCs molecule in a heat pipe. The presence of buffer gas (Ar) produced in the spectra the dense pattern of collision-induced rotation relaxation lines, thus enlarging the B(1)(1)Π data set, allowing to determine the Λ-splitting constants and to reveal numerous local perturbations. In total, 2664 term values for (85)Rb(133)Cs and (87)Rb(133)Cs in the energy range from 13,770 to 15,200 cm(-1) were obtained with accuracy about 0.01 cm(-1). A pointwise potential energy curve (PEC) based on inverted perturbation approach was constructed in the R-range from 3.35 to 9.00 Å for less perturbed vibrational levels v' ε [0, 35] and compared with ab initio calculations. The data included in the fit were reproduced by present PEC with standard deviation (sd) 0.95 cm(-1). More systematic over rotational levels J(') ε [6, 228] data set was obtained for v' ε [0, 2]. These data were reproduced by the obtained PEC with sd of 0.08 cm(-1). The energy of PEC's minimum Te = 13,746.65 cm(-1), as well as other main molecular constants were determined.

The reaction products of the 193 nm photolysis of vinyl bromide and vinyl chloride studied by time-resolved Fourier transform infrared emission spectroscopy

Time-resolved Fourier transform infrared (TRFTIR) emission spectroscopy has been used to study the 193 nm photolysis of vinyl bromide (C(2)H(3)Br) and vinyl chloride (C(2)H(3)Cl). Time-resolved IR emission was analysed to obtain nascent vibrational state populations of two primary photolysis products: HBr (v = 1-7) and HCl (v = 1-6). In both cases the nascent vibrational state populations monotonically decrease with increasing v and are in excellent agreement with previously published data. Time-resolved populations were analysed to yield rate constants for vibrational relaxation of HBr (v = 1-3) and HCl (v = 1-4) by parent vinyl bromide and vinyl chloride, respectively. In both cases the rate constants were found to increase with increasing vibrational quantum number, in agreement with a single quantum de-excitation via vibrational to vibrational energy transfer. Butadiene (C(4)H(6)) was identified as a secondary product of the photolysis of both vinyl halides, and shown to be formed from the reaction of parent vinyl halide with the vinyl radical. The presence of a buffer gas was found to produce a strong emission feature centred at 2,200 cm(-1), the intensity of which was dependent on the pressure of the buffer gas used, and whose kinetics are indicative of a secondary reaction product. We propose that this emission is from the vibrational progression of the electronic transition A(0, v, 1) --> X(0, v, 2) in the secondary reaction product C(2)H, whose formation route is favoured by the presence of buffer gas.

The effects of pulsed introduction of buffer gas on ion storage and detection efficiencies in a quadrupole ion trap

The quadrupole ion trap is commonly operated with a constant background pressure of an inert, low molecular weight buffer gas. This inclusion of a buffer gas has been shown to increase the sensitivity and mass resolution of the instrument. Research to gain an understanding of these effects, both experimental and through simulations, has typically assumed that it is optimal to maintain a constant buffer gas pressure throughout the entire experiment This article describes the effects of the pulsed introduction of buffer gas at strategic points within the analytical scan and evaluates those events during which the presence of buffer gas is critical. By incorporating a pulsed valve within the ion trap manifold, both the presence and pressure of the buffer gas can be controlled and varied during the individual steps of the scan. The presence of helium buffer gas just before the ion ejection and detection event showed a greater increase in intensity of the ion signal than at any other time in the analytical scan. In addition, this increase in intensity upon pulsed introduction of buffer gas prior to detection is constant over a wide range of pulsed valve open times (i.e., pressures), whereas the signal enhancement upon pulsed introduction of the buffer gas before ionization is observed only over a narrow range of pulsed valve open times.

Production ofYbH+by chemical reaction ofYb+in excited states withH2gas

It is known that fluorescence of trapped ${\mathrm{Yb}}^{+}$ ions fades with continuous driving of the $^{2}$ ${\mathrm{S}}_{1\mathrm{/}2}$${\mathrm{\ensuremath{-}}}^{2}$${\mathrm{P}}_{1\mathrm{/}2}$ transition in the presence of buffer gases. This phenomenon has been interpreted as being caused by population trapping in the $^{2}$ ${\mathrm{F}}_{7\mathrm{/}2}$ state of ${\mathrm{Yb}}^{+}$ . As another cause of the fluorescence disappearance, we found the production of ${\mathrm{YbH}}^{+}$ by chemical reaction of ${\mathrm{Yb}}^{+}$ in excited states with ${\mathrm{H}}_{2}$ gas. We found that the wavelengths of 369.482, 369.202, and 368.947 nm, formerly assigned as wavelengths for deexcitation of ${\mathrm{Yb}}^{+}$ in the $^{2}$ ${\mathrm{F}}_{7\mathrm{/}2}$ state to the $^{2}$ ${\mathrm{S}}_{1\mathrm{/}2}$ ground state, are actually photodissociation lines of ${\mathrm{YbH}}^{+}$ . The change of the resonance point of rf resonance absorption signals indicates the production and dissociation of ${\mathrm{YbH}}^{+}$ ions. The production of ${\mathrm{YbH}}^{+}$ may be a problem in establishing frequency standards using buffer-gas-cooled ${\mathrm{Yb}}^{+}$ , owing to difficulty in removing ${\mathrm{H}}_{2}$ gas from vacuum systems.

Collisional redistribution of energy in the infrared spectrum of potassium vapor under two-photon excitation

The cascade decay of the 6S(4D) levels of the potassium atom, 6S(4D)-5P-5S(3D)-4P, following two-photon excitation of potassium vapor (4S-4P-6S) is investigated experimentally. The dependences of 11 resonant IR line intensities on potassium and buffer gas densities are presented. It is shown that the presence of buffer gas leads to collisional redistribution of radiation, causing suppression of some lines and production of new ones.

Disappearance of Trapped Yb+

Abstract The storage time of Yb+ ions trapped in an r.f. trap was determined by the rf resonance absorption method in the presence of buffer gas, without and with laser radiation of a frequency equal to the transition from the S1/2 ground state to the excited P1/2 state. The storage time of the ions with the buffer gas (presure between 1 × 10−4 and 4·2 × 10−4 Pa) was several hours without the laser radiation; this period was shortened to several hundred seconds by irradiation with a 500 nW laser source. This phenomenon shows that the trapped Yb+ ions disappeared from the trap as a result of irradiation with the resonance laser light.

Selectivity enhancement in tritium isotope separation by multiple frequency multiple photon dissociation of the CTF3/CHF3 System

Isotope separation of tritium by multiple photon dissociation process in multiple frequency fields of a TEA-CO2 laser is reported for the first time. A ten-fold improvement in the bulk selectivity was obtained in 8.5 Torr CTF3/CHF3 in the presence of buffer gas at room temperature using 9R(8) to 9R(14) CO2 laser lines compared to single frequency excitation. Investigations of various process parameters such as exciting laser frequencies, pulse energy, sample and buffer gas pressure indicate that this is a promising technique for the separation of tritium.

The effect of hyperfine structure on the collisional relaxation of the thallium atom excited by laser beam

We present a theoretical analysis of the transient population inversions which appear in the optically pumped thallium (6 2 P 1/2 , 6 2 3/2 , 7 2 S 1/2 ) atom. We account for the hyperfine structure and we assume that the pumping occurs in the presence of buffer gas. Numerically computed time dependencies of population differences between the Zeeman sublevels of hyperfine levels of the 7 2 S 1/2 and 6 2 P 1/2,3/2 states are given. It is demonstrated how the described effects depend on the strength of the atom-field coupling and buffer gas pressure. The role of resonant and nonresonant pumping is explained

Unimolecular reactions in isolated and collisional systems: Deuterium isotope effect in the photoisomerization of stilbene

The isomerization of t-stilbene (stilbene h12 ) and three deuterated derivatives has been studied in a supersonic expansion, the thermal gas phase, and solution. In the jet we find that almost all effect of full deuteration (stilbene d12 ) is produced by deuteration of the two ethylinic hydrogens only (stilbene d2 ). Complete deuteration of the phenyl rings (stilbene d10 ) has rather little influence on the decay of the jet-cooled molecule. Nonexponential decays are found at intermediate excess energies in the jet-cooled system, with the degree of nonexponentiality decreasing with increasing excess energy. The ordering of the decay rates observed in the jet is not consistent with previous RRKM calculations of the isomerization rates of stilbene h12 and d2. Using similar parameters the calculations consistently place the stilbene d2 and stilbene d10 curves in the wrong order. Our results suggest extensive but not complete vibrational relaxation in the isolated molecule. Vibrational redistribution rapidly becomes complete in the presence of buffer gas. In thermal samples the isomerization rates of stilbene h12 and stilbene d10 are identical over a wide range of solvents and temperatures. By contrast the isomerization rates in stilbene d2 and stilbene d12 are 1.4 and 1.5 times slower than in stilbene h12. Again, these ratios appear constant over a wide range of experimental conditions.

Three-body collisions between laser-excited Na and K atoms in the presence of buffer gas

Energy pooling in alkali vapour mixtures has been previously investigated by us in an amalgam of sodium and potassium. In this paper we describe the peculiar features appearing when some buffer gas is introduced in the cell. We demonstrate that the buffer gas enhances the energy transfer between Na(3P) and K(4S), which is detected through the effects induced on the highly excited states populated by the Na(3P)/Na(3P) and K(4P)/K(4P) collisions.

The effect of hyperfine structure on the collisional relaxation of the Thallium atom excited by laser beam

We present a theoretical analysis of the transient population inversions which appear in the optically pumped thallium (62P1/2, 62P3/2, 72S1/2) atom. We account for the hyperfine structure and we assume that the pumping occurs in the presence of buffer gas. Numerically computed time dependencies of population differences between the Zeeman sublevels of hyperfine levels of the 72S1/2 and 62P1/2, 3/2 states are given. It is demonstrated how the described effects depend on the strength of the atom-field coupling and buffer gas pressure. The role of resonant and nonresonant pumping is explained.

Deuterium separation by multiphoton dissociation of dichlorofluoromethane

Absorption and dissociation probabilities of CHCl2F and CDCl2F were investigated by a pulsed CO2 laser in the wavenumber region of largest selectivity for deuterium. The absorption of CHCl2F, which is a difference band, can largely be suppressed by cooling. At 200 K and at 920 cm−1 absorption selectivities up to 4000 were found by extrapolation. In the presence of buffer gas, CDCl2F can be multiphoton excited nearly like a linear absorber (“harmonic oscillator”). This is interpreted by a nearly resonant collisional relaxation v7 to v2 and by the smallness of the cross anharmonicity x27. The dissociation selectivityS was 24,000 at natural abundance. Such large values were measured by a chromatographic method.S depends only onp D, the partial pressure of the deuterated species. This dependence is approximately ln S∝p D −1 . It can be rationalized by considering only the average energy transferred to the nonresonant molecules by collisions with CDCl2F. The above functional shape is related to an Arrhenius type law. Comparison with trifluoromethane for D separation shows that CHCl2F has primarily two advantages: its rapid H-D exchange with water and the less stringent requirements of laser energy and pulse length.

Influence of rotational relaxation on multiphoton dissociation of CF3Br in the presence of buffer gases

A study was made of multiphoton dissociation of the CF3Br molecule in the presence of various buffer gases (He, Ne, N2, Ar, Kr). The main mechanism of the influence of collisions on the dissociation process at low buffer gas pressures (pb < 100 Torr) was found to be rotational relaxation.

Studies of the blue-green fluorescence from iodine molecules excited by A 193 nm ArF laser

The fluorescence behavior of a molecular iodine band at 510 nm is presented. This band is excited when iodine molecules absorb the 193 nm radiation of an ArF laser in the presence of buffer gases. A comparison is made between this band and the well known 342 nm band of I 2.

Relaxation of optically oriented mercury atoms Hg 199, Hg 201 in the presence of buffer gases. (USSR)

Relaxation of optically oriented mercury atoms Hg 199, Hg 201 in the presence of buffer gases. (USSR)

〈S 0〉 Cs and 〈S 0〉 Rb relaxation in the presence of buffer gas and the spin exchange between Cs and Rb

〈 S 0〉 Rb and 〈 S 0〉 Cs relaxation is studied in the presence of buffer gas and spin exchange between Cs and Rb. Spin exchange collisions are found to equalize the relaxation rates of Rb and Cs polarization. This result is completely confirmed experimentally for the relaxation of the first diffusion mode.

Linear model of confinement of charged particles in a quadrupole r.f. field in presence of buffer gases

We consider the trapping of particles in a harmonic well in presence of a diluted buffer gas. We established in a simple case a stochastic model which can be extended to the confinement in a qudrupole r.f. field.

Collisional narrowing of infrared water-vapor transitions

Water-vapor absorption lines in the ν2 band involving transitions between states of high rotational energy have been found to undergo substantial collisional narrowing in the presence of buffer gases. Measurements were carried out near 5.35 μm, using tunable lead sulfide selenide semiconductor diode lasers.