Jacek Borysow

Collision-induced rototranslational absorption spectra of CH4-CH4 pairs at temperatures from 50 to 300 K

The zeroth, first, and second spectral moments of the rototranslational collision-induced absorption (RT CIA) spectra of hydrogen-helium mixtures are calculated from the fundamental theory, for temperatures from 40 to 3000 K. With the help of simple analytical functions of three parameters and the information given, the RT CIA spectra of H/sub 2/-He pairs can be generated on computers of small capacity, with rms deviations from exact quantum profiles of not more than a few percent. Such representations of the CIA spectra are of interest for work related to the atmospheres of the outer planets and cool stars. The theoretical spectra are in close agreement with existing laboratory measurements at various temperatures from about 77 to 3000 K. 28 references.

Modeling of pressure-induced far-infrared absorption spectra Molecular hydrogen pairs

Meyer et al. (1985) have calculated the accurate induced dipole moment function of H2-H2 from first principles, using highly correlated wave functions for the first time in such work. The present paper is concerned with the collision-induced translational-rotational absorption coefficient for molecular hydrogen pairs, taking into account computations on the basis of the fundamental theory considered by Meyer et al. Data have been obtained for temperatures in the range from 40 to 300 K. Criteria are developed for choosing among various model line shapes. It is found that certain models are capable of approximating the quantum profiles closely, with rms errors of only a few percent.

LASER-INDUCED BREAKDOWN SPECTROSCOPY FOR DETECTION OF LEAD IN CONCRETE

Time-resolved laser-induced breakdown spectroscopy was applied for quantitative measurement of lead content in concrete at levels down to 10 ppm. The breakdown was formed at the sample surface by a Q-switched ND:YAG laser operating at a 1.06-μm wavelength and a repetition rate of 10 Hz. Contamination levels were inferred from the ratio of the integrated emission line of lead to a known reference line of the matrix. The lead contamination can be determined on an absolute scale down to 10 ppm at an optimum delay time of 3.0 μs. These results were derived from analysis of the temporal evolution of the calibration function within a 0.1- to 19.0-μs time range. The calibration function exhibits no dependence on the incident laser pulse energy, which was varied from 250 to 400 mJ.

Vibrational and rotational excitation within the X 1Σ state of N2 during the pulsed electric discharge and in the afterglow

The time transients of vibrational/rotational excitation up to v = 6 level of the ground electronic state of nitrogen were measured in a positive column during the 1 µs pulsed electric discharges, and in the afterglow. The peak current densities were up to 25 A cm−2 at the gas pressure of 5 Torr. During the active discharge the energy was transferred mainly into vibrational levels, primarily above v = 1, resulting in highly non Boltzmann distribution. The vibrational distribution became Boltzmann-like approximately 80 µs after the discharge pulse and remained of this character until the next pulse. Rapid rotational heating was observed immediately following the cessation of the discharge current. The rotational temperature had risen from about 300 K during the discharge to more than 3000 K within the first 80 µs of the afterglow and returned later to ambient (300 K) in less than 100 µs. Its peak coincided with the time when the redistributed vibrational populations closely resembled the Boltzmann distribution. The vibrational populations could be described by a single temperature (approximately 3000 K) from 100 µs till nearly 1 ms after the discharge. All vibrational bands could be well described by the same rotational temperature at all times. Standard, coherent anti-Stokes Raman spectroscopy was used in all measurements.

Direct spectroscopic detection of A′ 5Σ+g state of N2

Abstract The A′ 5 Σ + g state of N 2 was detected for the first time in a direct measurement, using a high-resolution laser absorption technique within the C″ 5 Π u ← A′ 5 Σ + g (ν′ = 0 ← ν″ = 0) band. Evidence is given that the quintet state was created by means of an energy pooling reaction from the A 3 Σ + u state in a pure nitrogen pulsed discharge. From the absolute density measurements of the quintet A′ state and its precursor triplet A state, the upper limit for the destruction rate coefficient of the A′ 5 Σ state by a ground state molecular nitrogen was estimated to be 7 X 10 −12 cm 3 molecule −1 s −1 .

Long-range tunable diode laser

A novel, simple tuning mechanism for single-mode, pseudo-external-cavity diode lasers has been developed. The model calculations predict that the laser can be tuned continuously by as much as 300 GHz in the vicinity of the chosen frequency without locking it to an external cavity. Experimentally, the continuous tuning range is approximately 120 GHz at constant current and temperature for the 7-cm-long pseudo-external cavity; this is several times more than previously reported. A turning wedge inside the laser cavity is used as the tuning element. The laser is based on a commercial laser diode chip, and a diffraction grating is used for feedback. The total tuning range depends on the laser diode type and can be up to 20 nm.

N2(a‘ 1Σg+) metastable collisional destruction and rotational excitation transfer by N2

Quenching and rotational coupling rate coefficients have been measured for the J=4–10, v=0 levels of the a‘ 1Σg+ metastable state of N2 in collisions with ground state N2. Laser absorption is used to monitor the population of rotational levels of the a‘ 1Σg+ state following depletion of the population of one or more levels by optical pumping to other states. The observed time dependence of the recovery of population of the perturbed level and the collision induced growth and decay of the populations of adjacent levels are interpreted in terms of quenching to other electronic levels and excitation exchange among adjacent rotational levels. For the J=6, v=0 level of the a‘ 1Σg+ state the rate coefficients extrapolated to zero discharge current at 300 K are 2.3±0.1×10−16 m3/s for electronic quenching and 1.1±0.6×10−16 m3/s for excitation transfer to the J=4 and J=8 levels in collisions with N2. Very similar rate coefficients were obtained for the J=4, 7, and 8 levels.

Spatial distributions of absolute densities of argon metastable state 3p54s in a Gaseous Electronics Conference Reference Cell

The spatial distributions of the 3p54s metastable state of Ar have been measured in radio frequency argon plasmas in a Gaseous Electronics Conference Reference Cell by means of high resolution absorption spectroscopy. A single-mode, tunable diode laser has been used to obtain absorption profiles at 750 and 801 nm. Spatial profiles across the gap between electrodes have been measured with 1 mm resolution for various pressures (0.15–1.0 Torr) and plasma powers (1–320 W). The densities of 3p54s metastable were obtained from integrated absorption profiles.

Spectroscopic and thermodynamic properties of molecular hydrogen dissolved in water at pressures up to 200 MPa

We have measured the Raman Q-branch of hydrogen in a solution with water at a temperature of about 280 K and at pressures from 20 to 200 MPa. From a least-mean-square fitting analysis of the broad Raman Q-branch, we isolated the contributions from the four lowest individual roto-vibrational lines. The vibrational lines were narrower than the pure rotational Raman lines of hydrogen dissolved in water measured previously, but significantly larger than in the gas. The separations between these lines were found to be significantly smaller than in gaseous hydrogen and their widths were slightly increasing with pressure. The lines were narrowing with increasing rotational quantum number. The Raman frequencies of all roto-vibrational lines were approaching the values of gas phase hydrogen with increasing pressure. Additionally, from the comparison of the integrated intensity signal of Q-branch of hydrogen to the integrated Raman signal of the water bending mode, we have obtained the concentration of hydrogen in a solution with water along the 280 K isotherm. Hydrogen solubility increases slowly with pressure, and no deviation from a smooth behaviour was observed, even reaching thermodynamic conditions very close to the transition to the stable hydrogen hydrate. The analysis of the relative hydrogen concentration in solution on the basis of a simple thermodynamic model has allowed us to obtain the molar volume for the hydrogen gas/water solution. Interestingly, the volume relative to one hydrogen molecule in solution does not decrease with pressure and, at high pressure, is larger than the volume pertinent to one molecule of water. This is in favour of the theory of hydrophobic solvation, for which a larger and more stable structure of the water molecules is expected around a solute molecule.

SINGLE-MODE TUNABLE TI:SAPPHIRE LASER OVER A WIDE FREQUENCY RANGE

We report a design of a tunable Ti:sapphire laser capable of operating in the range between 700 and 800 nm. The continuous, single-mode tuning is achieved by a pseudoexternal cavity consisting of highly reflective mirrors and a diffraction grating. The advantages of this laser include low operational threshold, a simple configuration that involves only four optical elements, and fine-tuning capabilities. The single longitudinal mode of operation was demonstrated at wavelengths between 695 and 725 nm and was limited by the choice of end mirrors in the laser cavity.