Angular distributions are measured for individually resolved ν′, j′ states of HF produced by F + H 2 f HF(ν′ ) 1, j′) + H and F + H 2 f HF(ν′)2, j′) + H reactive collisions in a crossed-beams scattering apparatus. Simultaneous resolution of the HF vibrational and rotational states is achieved spectroscopically for the first time, using laser excitation in conjunction with bolometric detection. The technique is sensitive to population differences between ν′ ) 1, j′ and ν′ ) 2, j′ -1 states optically coupled by specific P 2 (j′) lines of a vibrotational chemical laser. The measurements are greatly facilitated by the development of a new high-temperature atomic fluorine beam source, which exhibits excellent stability, very high intensity, and narrow velocity distributions. Features common to individual product rotational states are as follows: strong backward scattering into ν′ ) 2, j′; weaker backward scattering into ν′ ) 1, j′; and heretofore unobserved scattering into ν′ ) 1, j′ in the forward hemisphere. These angular distributions agree qualitatively with predictions from fully three-dimensional exact quantum reactive scattering calculations (Castillo et al., J. Chem. Phys. 1996, 104, 6531) that were conducted on an accurate potential energy surface (Stark and Werner, J. Chem. Phys. 1996, 104, 6515). However, quasi-classical calculations conducted on the same potential energy surface do not produce any substantial forward-scattered HF in ν′ ) 1 (Aoiz et al., Chem. Phys. Lett. 1994, 223, 215), suggesting that its appearance in the forward hemisphere may be a quantum effect. The quantum theoretical cross-sections also suggest that the forward ν′ ) 1 products arise almost entirely from H 2 reactants initially in j ) 1.

International audiencePrecision ultrasonic measurements in binary gas systems provide continuous real-time monitoring of mixture composition and flow. Using custom microcontroller-based electronics, we have developed sonar instruments, with numerous potential applications, capable of making continuous high-precision sound velocity measurements. The instrument measures sound transit times along two opposite directions aligned parallel to - or obliquely crossing - the gas flow. The difference between the two measured times yields the gas flow rate while their average gives the sound velocity, which can be compared with sound velocity vs. molar composition look-up curves to obtain the binary mixture at a given temperature and pressure. The look-up curves may be generated from prior measurements in known mixtures of the two components, from theoretical calculations, or from a combination of the two. We describe the instruments and their performance within numerous applications in the ATLAS experiment at the CERN Large Hadron Collider (LHC). The instruments can be of interest in other areas where continuous in-situ binary gas analysis and flowmetry are required

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A novel gas nozzle design that allows for collinear laser and molecular beams is described. Unlike conventional nozzles that open and close to limit the gas flow into a vacuum chamber, this nozzle opens to release a small volume of gas into the chamber. Gas pulses of 300 μs duration and 65±5 μs opening times have been obtained. When room-temperature H2 is used as the source gas, the rotational temperature was found to be 175±12 K, whereas when room-temperature D2 was used, the rotational temperature was found to be 104±7 K. The collinear optical and molecular beam path provided in this design may be useful in photodissociation experiments, the study of atomic and molecular collisions, Rydberg state lifetime measurements, and vacuum ultraviolet generation by nonlinear mixing in gases.

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