Infrared spectrum and stability of a π-type hydrogen-bonded complex between the OH and C2H2 reactants

A hydrogen-bonded complex between the hydroxyl radical and acetylene has been stabilized in the reactant channel well leading to the addition reaction and characterized by infrared action spectroscopy in the OH overtone region. Analysis of the rotational band structure associated with the a-type transition observed at 6885.53(1) cm−1 (origin) reveals a T-shaped structure with a 3.327(5) Å separation between the centers of mass of the monomer constituents. The OH (v = 1) product states populated following vibrational predissociation show that dissociation proceeds by two mechanisms: intramolecular vibrational to rotational energy transfer and intermolecular vibrational energy transfer. The highest observed OH product state establishes an upper limit of 956 cm−1 for the stability of the π-type hydrogen-bonded complex. The experimental results are in good accord with the intermolecular distance and well depth at the T-shaped minimum energy configuration obtained from complementary ab initio calculations, which were carried out at the restricted coupled cluster singles, doubles, noniterative triples level of theory with extrapolation to the complete basis set limit

Evidence for partial quenching of orbital angular momentum upon complex formation in the infrared spectrum of OH-acetylene

The entrance channel leading to the addition reaction between the hydroxyl radical and acetylene has been examined by spectroscopic characterization of the asymmetric CH stretching band of the π-hydrogen bonded OH-acetylene reactant complex. The infrared action spectrum observed at 3278.6 cm−1 (origin) consists of seven peaks of various intensities and widths, and is very different from those previously reported for closed-shell HF/HCl-acetylene complexes. The unusual spectrum arises from a partial quenching of the OH orbital angular momentum in the complex, which in turn is caused by a significant splitting of the OH monomer orbital degeneracy into 2A′ and 2A″ electronic states. The magnitude of the 2A′−2A″ splitting as well as the A rotational constant for the OH-acetylene complex are determined from the analysis of this b-type infrared band. The most populated OH product rotational state, jOH = 9/2, is consistent with intramolecular vibrational energy transfer to the ν2 C≡C stretching mode of the departing acetylene fragment. The lifting of the OH orbital degeneracy and partial quenching of its electronic orbital angular momentum indicate that the electronic changes accompanying the evolution of reactants into products have begun to occur in the reactant complex

THE CONVERSION OF STYRENE OXIDE ENANTIOMERS INTO SPECTROSCOPICALLY DISTINGUISHABLE DIASTEREOMERS THROUGH COMPLEXATION WITH 3,3,3-TRIFLUORO-1,2-EPOXYPROPANE

3,3,3-Trifluoro-1,2-epoxypropane [2-(trifluoromethyl)-oxirane, or TFO] has shown promise as a tag for chiral analysis through conversion of enantiomers into spectroscopically distinguishable diastereomers via the formation of non-covalently bound heterodimers. We demonstrate the suitability of this method through characterization of the microwave rotational spectrum of complexes formed between TFO and styrene oxide (SO). Molecular dynamics calculations are used to quickly identify possible heterodimer conformations which are then optimized and evaluated using density functional theory. Using a mixture of racemic samples of both species, we observe and assign spectra for the lowest energy conformers of both homochiral (RR/SS)-TFO-SO and heterochiral (RS/SR)-TFO-SO. Had a single enantiomer of TFO been used, say (R), the spectra are sufficiently distinct and sufficiently well predicted by theory that (RR)-TFO-SO and (RS)-TFO-SO are readily identified and separately analyzed

THE MICROWAVE SPECTRUM AND MOLECULAR STRUCTURE OF THE CHIRAL TAGGING CANDIDATE, 3-FLUORO-1,2-EPOXYPROPANE (EPIFLUOROHYDRIN), AND ITS COMPLEX WITH THE ARGON ATOM

Continuing our efforts in characterizing small molecules for use as potential chiral tags for the conversion of enantiomeric molecules into spectroscopically distinct diastereomeric complexes for chiral analysis, we examine the microwave spectrum and molecular structure of 3-fluoro-1,2-epoxypropane. Although this species has a lower vapor pressure than the trifluoro- and difluoro- analogues previously reported at this meeting, it is still relatively easy to incorporate into a free jet expansion by flowing a carrier gas over a heated liquid sample. In common with the structurally similar trifluoro- and difluoro- species, it has a simple, hyperfine-free rotational spectrum. This spectrum has been obtained for the most abundant and four singly-substituted isotopologues, all in natural abundance, and the structure of the molecule determined. Multiple minima of similar energies are predicted for the complex of 3-fluoro-1,2-epoxypropane with argon, and progress on assigning and analyzing the spectra of these complexes will be reported

Microwave spectrum and molecular structure of the argon-cis-1,2-dichloroethylene complex

The non-planar molecular structure of the complex formed between the argon atom and {\it cis}-1,2-dichloroethylene is determined via analysis of its microwave spectrum. Spectra of the $^{35}$Cl and $^{37}$Cl isotopologues are observed in natural abundance and the nuclear quadrupole splitting due to the two chlorine nuclei is fully resolved. In addition, the complete quadrupole coupling tensor for the {\it cis}-1,2-dichloroethylene molecule, including the single non-zero off-diagonal element, has been determined. Unlike the argon-{\it cis}-1,2-difluoroethylene and the argon-vinyl chloride complexes, tunneling between the two equivalent non-planar configurations of argon-{\it cis}-1,2-dichloroethylene is not observed

Propulsion System Modeling and Takeoff Distance Calculations for a Powered-Lift Aircraft with Circulation-Control Wing Aerodynamics

The computation of takeoff distance for powered-lift aircraft is complicated because of the coupling of aerodynamic performance (lift, drag and moment coefficients) with forward speed. Cal Poly has developed an analysis procedure to capture this coupling, and the development of this procedure is continuing. In the past year, Cal Poly has completed a Phase I NRA contract from the NASA for the configuration development and modeling of CESTOL aircraft. The primary objective of this contract was to identify an aircraft configuration in enough detail to proceed into a Phase II contract to design and construct a large scale wind tunnel model followed by a wind tunnel test to measure both aerodynamic performance and noise. Four aircraft configurations have been developed, and all but one of the configurations use circulation control wing aerodynamics (CCW) to produce powered-lift aerodynamic effect for the wing. The aircraft configuration selected for the Phase II contract makes extensive use of CCW to develop high lift aerodynamics for takeoff and initial climb and again for final descent and landing. An additional goal for the Phase I project was the CFD modeling of the aerodynamics of a CESTOL aircraft, and to use the CFD results to develop a new aerodynamic meta-model. In addition, a meta-model for propulsion performance was to be developed and the two meta-models were to be integrated into an upgraded takeoff code written in MATLAB. These models all combined were to demonstrate an up-graded version of the Cal Poly takeoff performance procedure. However, at present, the aerodynamics meta-model is not yet complete and work will continue on into Phase II. Thus, no specific takeoff performance is demonstrated in this paper. However, in this paper details of the aircraft configurations are presented, the options available to proceed high pressure air to the wing slots to produce CCW aerodynamics are discussed, the propulsion metamodel is defined, the analysis procedure for the aerodynamics meta-model is discussed and the up-graded takeoff program is discussed

Review Of Aerodynamically Induced Forces Acting On Centrifugal Compressors, And Resulting Vibration Characteristics Of Rotors

TutorialThere are several sources of non-synchronous forced vibration of centrifugal compressor rotors. Many of them are aerodynamic phenomena, created within the gas path of the compressor. Phenomena such as impeller stall, diffuser stall (with and without vanes), and flow instabilities caused by impeller to diffuser misalignment, are all characteristic flow disturbances that can cause forced vibration. In fact, often the only indications of these phenomena are found in the resulting rotor vibration signals. Several phenomena that can cause non-synchronous vibration are reviewed, and for each one, background information, as well as detailed descriptions of the flow field, or other source of the excitation, is provided. This includes the use of CFD analytical results to describe the flow where applicable. The review also includes, when available, dynamic pressure transducer test data that can be used to verify the presence of the phenomena, and rotor vibration data indicating the presence of such phenomena. This includes test data of actual machines, indicating characteristics such as frequency and amplitude