Robert L. Cook

Molecular force field and structure of water: Recent microwave results

Abstract Recently, microwave studies of the rotational spectra of water and its various isotopic species have been reported. These studies provide rotational constants and among others the quartic distortion constants, which depend on the quadratic part of the vibrational potential function. These data are collected and discussed, and the molecular force field and structure of water is considered in light of this recent microwave data. The quartic distortion data gives force constants which are very reasonable considering the difficulties in the distortion analysis of these light molecules, where as many as 22 parameters are being evaluated to fit the observed spectrum. The infrared and microwave data are combined within the theoretical framework of the small oscillations model and the results compare favorably with the true harmonic force field. The infrared and microwave valence bond force constants of H 2 O are (mdyn/A): ƒ r =7.746, ƒ θ =0.700, ƒ rr =−0.093, ƒ rθ =0.379 The results further confirm the usefulness of rotation-vibration data in the determination of force constans, and show that even for water with extremely large anharmonicity effects, a very representative force field can be obtained by combining ground state infrared and microwave data. Various molecular structures have been evaluated, and the average structures in the ground vibrational state for H 2 O, D 2 O and T 2 O are found to be: 〈r〉 〈θ O-H=0.9724 A HOH=104.50° O-D=0.9687 A DOD=104.35° O-T=0.9671 A TOT=104.26° A one-dimensional approximation to the anharmonicity effects is applied to determine the equilibrium molecular structure of H 2 O from the average structure data. The result is as follows: r e =0.9587 A and θ e =103.9°

Molecular force field and structure of hydrogen sulfide: recent microwave results

Abstract Recently, microwave studies of the rotational spectra of hydrogen sulfide and its various isotopic species have been reported. These studies provide accurate rotational constants and, among others, the quartic distortion constants, which depend on the quadratic part of the vibrational potential function. These data are collected and the molecular force field and structure of hydrogen sulfide are considered in light of these recent microwave data. The infrared and microwave data are combined within the theoretical framework of the small oscillations model and the results compare favorably with the true harmonic force field. The IR & MW valence bond force constants of H2S are (md A−1): fr = 3.988, fθ = 0.399, frr = −0.017, frθ = 0.057. The results further confirm the usefulness of rotation-vibration data in the determination of force constants, and show that even with large anharmonicity effects a very representative force field can be obtained by combining ground state infrared and microwave data. Various molecular structures have been evaluated, and the average structures in the ground vibrational state for H2S and D2S are found to be: S-H = 1.3518 A HSH = 92.13° S-D = 1.3474 A DSD = 92.11° A one-dimensional approximation to the anharmonicity effects is applied to determine the equilibrium structure of H2S from the average structure data. The result is as follows: re = 1.3362 A and θe = 92.06° This bond distance is some 0.0006 A larger than that obtained by applying the vibrational corrections measured in the infrared region [4].

Laser-Induced Breakdown Spectra in a Coal-Fired MHD Facility

A study of laser-induced breakdown spectroscopy (LIBS) has been performed in a particle-loaded methane/air flame and in the Diagnostic Instrumentation and Analysis Laboratory/Mississippi State University (DIAL/MSU) test stand to evaluate its application for practical environments. The LIBS spectra collected from different observational directions and spectral regions are compared. The forward LIBS technique has been chosen to characterize the upstream region of a large magnetohydrodynamics (MHD) coal-fired flow facility (CFFF). The relative concentrations of several species are inferred by fitting the observed CFFF LIBS spectra with computer-simulated spectra. This paper reports the first LIBS experiments in a harsh, turbulent, and highly luminous coal-fired MHD combustion environment.

Study of optical emission from laser-produced plasma expanding across an external magnetic field

The laser-induced plasma obtained from the liquid target and expanding across a steady magnetic field has been studied using atomic emission spectroscopy. The line emission from the plasma was enhanced (> 1.5 times) in the prese nce of a magnetic field, whereas background emission decreases. Enhancement in line intensity was found to be mi.inly a function of plasma beta (F). An increased rate of three-body recombination in plasma particles due to the cooling of the plasma during its expansion and an increase in effective plasma density as a result of its confinement seems to be the reason behind this enhancement.

The molecular conformation and dipole moment of thiane from the microwave spectrum

Abstract The microwave spectrum of thiane, a heterocyclic analog of cyclohexane, has been studied in the region 26.5–40 GHz. The molecule is a highly asymmetric rotor (κ = 0.050154). From the analysis of both the a -type and c -type transitions, the rotational constants determined are (in MHz): A = 3992.719, B = 3005.812, and C = 1914.683. A study of the Stark effect has yielded the dipole moment components (in Debye units) μ a = 1.684 ± 0.009, μ c = 0.578 ± 0.002, which give a total dipole moment of μ = 1.781 ± 0.010. Comparison of the spectral data from tetrahydropyran, thiane, and 1,4-thioxane demonstrates the similarity in structure of these three compounds. It is found that a very reasonable set of structural parameters can be found which adequately fits the spectral data of all three molecules.Abstract The microwave spectrum of thiane, a heterocyclic analog of cyclohexane, has been studied in the region 26.5–40 GHz. The molecule is a highly asymmetric rotor (κ = 0.050154). From the analysis of both the a -type and c -type transitions, the rotational constants determined are (in MHz): A = 3992.719, B = 3005.812, and C = 1914.683. A study of the Stark effect has yielded the dipole moment components (in Debye units) μ a = 1.684 ± 0.009, μ c = 0.578 ± 0.002, which give a total dipole moment of μ = 1.781 ± 0.010. Comparison of the spectral data from tetrahydropyran, thiane, and 1,4-thioxane demonstrates the similarity in structure of these three compounds. It is found that a very reasonable set of structural parameters can be found which adequately fits the spectral data of all three molecules.

Low resolution microwave spectra and indo calculations of phenylisothiocyanate and phenylisocyanate

Abstract The low resolution spectra of φNCS and φNCO have been studied in the microwave R-band region. The spectroscopic constant ( B + C ) has been evaluated for both molecules. These data have been used to obtain information on the orientation of the linear NCS and NCO group relative to the bond from the phenyl ring. The results indicate an opening of the φ-N-C angle over that found in the hydrogen counterparts HNCS and HNCO. A modified INDO calculation yields structural parameters which are consistent with the trends observed, and indicate that the opening of the angle in going from HNCS (HNCO) to φNCS (φNCO) can be attributed to delocalization with the phenyl ring.

Laser-Induced Breakdown Spectroscopy of Hydrocarbon Flame and Rocket Engine Simulator Plume

Laser-induced breakdownspectroscopy (LIBS) ofmetal-seeded aerosols and a hydrocarbon flame werestudied t o determine the pmper experimental condition for rocket motor application. LIBS and atomic emission spectroscop y (AES) were also performed in the rocket motor simulator to evaluate both technologies for the health monitorir g of the rocket engine. The LIBS signal of the seeded element goes down drastically in the presence of the flame i n comparison to the signal obtained from the aemsols of the elements. Similarly the LIBS signal of the trace elemen is was very weak in the luminous flame and the simulator plume in comparison to the messurement outside iL Tlre intensity of the LIBS signal from the trace elements pr€s€nt in the plume/flame was iound to be dependent on tlc process of seeding, the transition probabilitS and the decay time of the background emission. Ultimately LIBS wrs found to be more sensitive than AES in detecting the trace elements in the simulator plume. This study establish,s LIBS as an improved health-monitoring system over AES for the plume studied.

The microwave spectrum and conformation of 1,3‐cycloheptadiene

The microwave spectrum of 1,3‐cycloheptadiene has been studied. The ground state and a number of excited vibrational states have been assigned and the rotational constants evaluated. A study of the Stark effect has yielded the dipole moment components for the ground state and two of the excited vibrational states. The total dipole moment for the ground state is 0.740 D. These data have been used to determine the conformation of 1,3‐cycloheptadiene. The carbon skeleton is planar except for the C6 carbon atom (Cs form).

Spontaneous anti-Stokes Raman probe for gas temperature measurements in industrial furnaces

A compact, pulsed Nd:YAG laser-based instrument has been built to measure in situ absolute gas temperatures in large industrial furnaces by use of spontaneous anti-Stokes Raman scattering. The backscattering configuration was used to simplify the optics alignment and increase signal-to-noise ratios. Gated signal detection significantly reduced the background emission that is found in combustion environments. The anti-Stokes instead of the Stokes component was used to eliminate contributions to spectra from cold atmospheric nitrogen. The system was evaluated in a methane/air flame and in a bench-top oven, and the technique was found to be a reliable tool for nonintrusive absolute temperature measurements with relatively clean gas streams. A water-cooled insertion probe was integrated with the Raman system for measurement of the temperature profiles inside an industrial furnace. Gas temperatures near 1500-1800 K at atmospheric pressure in an industrial furnace were inferred by fitting calculated profiles to experimental spectra with a standard deviation of less than 1% for averaging times of approximately 200 s. The temperatures inferred from Raman spectra are in good agreement with data recorded with a thermocouple probe.

Centrifugal distortion effects in the microwave spectrum of methylene cyanide

Abstract The rotational spectrum of methylene cyanide has been measured up to J = 62 and a total of 82 b-type transitions have been obtained. These data have been analyzed with a semirigid rotor Hamiltonian to give accurate rotational and centrifugal distortion constants. The rotational constants are (in MHz) A = 20882.7537 ≠ 0.017, B = 2942.3003. ≠ 0.0031, C = 2616.7225 ≠ 0.0031 The quartic centrifugal distortion constants are (in MHz) Δ J (1.855455 ≠ 0.014) x 10 −3 Δ JK = (−6.79218 ≠ 0.027) x 10 −2 Δ K (8.621628 ≠ 0.013) x 10 −1 δ J = (4.892607 ≠ 0.016) x 10 −4 δ K = (6.7501 ≠ 0.29) x 10 −3 The uncertainties are twice the standard deviations in the constants obtained from the least squares analysis, and represent approximately 95% confidence limits.