Joe Kurtz

Combined infrared and ultraviolet‐visible spectroscopy matrix‐isolated carbon vapor

Infrared and UV‐visible absorption spectra have been measured on the same sample of matrix‐isolated carbon vapor in order to establish correlations between absorption intensities of vibrational and electronic transitions as a function of sample annealing. A high degree of correlation has been found between the IR feature at 1998 cm−1 recently assigned to C8 and a UV absorption feature at about 3100 A. Thus, for the first time, direct evidence is given for the assignment of one of the unknown UV‐visible features of the long‐studied matrix‐isolated carbon vapor spectrum.

A computational response to the C7 experimental challenge: low-energy C2v isomer

Abstract Recent experimental evidences of C7 cluster isomerism are supported by the second-order Moler—Plesset (MP2) perturbation treatment with the 6-31G* basis set. In addition to traditional linear structure, an elongated cyclic species of C2v symmetry represents another minimum energy structure located about 9 kJ/mol above the linear one (the MP4 energy separation in the MP2 geometry is 73 kJ/mol). Calculated structure and energetics is completed with harmonic vibrational analysis including isotope effects.

The solubility of oxygen in liquid iron oxide during the combustion of iron rods in high-pressure oxygen

Abstract The combustion of pure iron rods in oxygen is characterized by excess oxygen in the molten products. The amount of oxygen dissolved in the molten mass exceeds that required for stoichiometric haematite, Fe 2 O 3 , the highest oxidation state for solid iron oxide. Oxygen mass-balance calculations and post-test product analysis suggest that the average oxygen-to-iron molar ratio of the molten oxide product is as high as 2.1 and possibly higher. This corresponds to an increase in oxygen solubility in the molten iron oxide (over that of molten iron metal), which is compatible with the existence of various forms of ferrite ions such as FeO 2 −1 , Fe 2 O 5 −4 , FeO 3 −3 , and Fe 2 O 7 −8 . The presence of this excess oxygen confirms the proposed heterogeneous mechanism for the burning of iron, that is, that primary oxidation takes place at an interface between liquid iron and the molten combustion products containing the excess oxygen.

Theoretical studies of C5 with first-order correlation orbitals and the coupled cluster method

Abstract The many-body perturbation theory and the coupled cluster method with first-order correlation orbitals are used to study the structure of the linear C5 molecule. Calculations produce the equilibrium geometry with the outer and inner bond lengths equal to 1.294 and 1.287 A, respectively. This corresponds to the equilibrium rotation constant, Be, of 0.08442 cm−1.

Emission spectra of burning iron in high-pressure oxygen

Abstract Emission spectra of burning vertical iron rods in high-pressure oxygen were taken and correlated with the different stages of the burn evolution. By applying the least squares method to the spectral curves, the corresponding equivalent blackbody temperatures were computed. Based on the assumption of a wavelength-independent emissivity between 495 and 780 nm, it was found that the surface-averaged temperatures of the molten iron/iron oxide droplets ranged from a minimal value of ∼ 2500 K to a maximum value of ∼ 3900 K (in 1630 kPa O2) and the temperatures increased with the size (and age) of the droplets.

Inversion of the C8 non-planar ring

Abstract Inversion of the recently reported non-planar cyclic minimum-energy structure of C 8 (D 2d symmetry) is studied by means of the second-order Moller-Plesset perturbation treatment with the 6-31G * basis set. Two new planar cyclic saddle points have been found, possessing D 4h and C 2h symmetry and exhibiting two and one imaginary frequencies, respectively. The former and the latter saddle point are located 71 and 54 kJ/mol, respectively, above the D 2d minumum. Calculated harmonic vibrational frequencies for the activated complex C 2h are presented.

Baseline correction for stray light in log-ratio diode laser absorption measurements.

Log-ratio detection is a convenient technique for making temperature and concentration measurements using sensors based on tunable diode laser absorption spectroscopy. In many practical sensing applications, it is difficult to avoid stray light falling on the signal photodiode of the sensor. This stray light acts as noncommon-mode interference and introduces a systematic error in absorption measurements, which is not removed by baseline subtraction. This paper analyzes the factors that determine this systematic error and also presents a calibration method that can correct for it. This correction method is verified using a simple experiment.

Near-infrared absorptions of monomethylhydrazine

Abstract The peak absorption coefficients for two near-infrared absorptions of monomethylhydrazine, CH 3 -N 2 H 3 , (MMH) were measured. Absorption bands located at 1.524 μm (6560 cm -1 ), 1.557 μm (6423 cm -1 ), and 1.583 μm (6316 cm -1 ) are assigned to the △υ = 2 overtones of the infrared N-H stretching fundamentals at 3317, 3245 and 3177 cm -1 . An absorption band located at 1.04 μm (9620±100 cm -1 ) is assigned to the △υ = 3 overtone of one of these fundamentals. The peak absorption coefficients (α 10 ) at 1.524 μm (6560±20 cm -1 ) and 1.04 μm (9620±100 cm -1 ) are 31 × 10 -3 and 0.97 × 10 -3 (cm atm) -1 , respectively. Uncertainties in these coefficients were estimated to be less than ±20% due primarily to uncertainties in the partial vapor pressure of MMH.

Flight test of a rugged scramjet-inlet temperature and velocity sensor

The performance of a gas temperature and velocity sensor based on tuneable diode laser absorption spectroscopy (TDLAS) of oxygen in a scramjet engine inlet during a flight test is discussed. This is the first flight-tested TDLAS sensor designed specifically for measuring gas velocity of a scramjet inlet flow under flight conditions. The robustness and stability of the sensor design in dynamic load conditions were made evident by the quality of the data delivered after a very unstable and high-g launch scenario. The scramjet did not reach the targeted test altitude-velocity regime. However, analysis of the low-altitude data determined pressure and temperature in the inlet and showed that an adequate signal-to-noise ratio was obtained for high-speed velocity measurements at altitudes up to at least 30 km.

Thermal-structural modelling of TDLAS system for SCRAMSPACE hypersonic flight test

A thermal-structural analysis of the TDLAS (Tunable Diode Laser Absorption Spectroscopy) system used on the SCRAMSPACE mission was performed to determine the integrity of the in-flight experiment when subjected to descent heat loads. This analysis is essential for the design of optical sensing equipment, which needs to survive the high temperatures generated in hypersonic flight. Firstly, in-flight temperatures reached by critical electro-optical components due to viscous heating were determined. In addition, the structural viability of the sapphire optical window was analysed to ensure it surpassed requirements at flight heating conditions. Lastly, the effect that in-flight heating has on the optical alignment of the system is currently being investigated. It was found that electronic components will operate within recommended temperature bounds. In addition, numerical and experimental analysis verified the flight worthiness and seal integrity of the sapphire window when subjected to the simulated hypersonic flight conditions.