The study of “Stereodynamics” aims at clarifying the role of molecular orientation upon reactivity at the atomic and molecular levels by experiment and theory. Rate of chemical reaction k(T) on the other hand is the most important quantity in macroscopic chemical world, and Arrhenius equation eventually explains its temperature dependence, where the steric factor appears in the pre-exponential factor A, regarded as an independent parameter from Boltzmann energy distribution. Therefore, “Stereodynamics” stands on a quite different viewpoint from energy-based, but rather from angular and linear momentum-based arguments for understanding chemical reactions. Secondly, even in complex systems such as gas-surface heterogeneous and enzyme catalyzed reactions, we see often that the effect of molecular orientation gains decisive power and control the overall complex reaction. This clearly manifests the very importance of molecular orientation or “Stereodynamics” in any collision event and chemical reaction.

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  A special class of molecules, symmetric tops such as CH₃Br, has dipole moments that are not averaged to zero as the molecules rotate. “Up” and “down” orientations of these molecules in a weak electric field have different energies and these orientations can be separated in an inhomogeneous electric field. Using such an inhomogeneous field, we have produced molecular beams oriented in space and have studied how this orientation affects chemical reactivity. Orientation is important. In the experiments discussed, an electron is transferred from a donor alkali atom to the LUMO of an oriented molecule. The stereochemistry of the transfer depends on the spatial extent of the LUMO, but the detection of the product (and the identity of the product) depends on the energy and the location of the donor.

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  Advances in experimental vacuum technology allow the generation of molecular beams containing oriented molecules. We will focus our review on the so-called collisional alignment, a molecular polarization phenomenon occurring in supersonic expansions of gaseous mixtures. The key feature is the velocity dependence of the alignment degree, which allows the use of mechanical devices to select the molecules of the beam having either a random or a preferential spatial distribution of their rotational angular momentum with respect to the molecular beam axis. The physical mechanisms underlying the collisional alignment will be outlined and some relevant gas-phase experiments demonstrating its occurrence will be illustrated permitting the applications of these tools to the study of elementary processes occurring both in homogeneous and heterogeneous phases. Investigation of the stereodynamics of elementary processes provides the background for perspective demonstration of manifestation of chiral effects in molecular collisions. This latter topic, in view of its fundamental relevance and also of interest in a protobiological context, is elaborated in some detail in this review.

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  In this review, we report our recent studies on the steric effect in the gas phase reaction which has been performed by using the oriented molecular and atomic beams. The preparation of the molecular orientation and the atomic orientation by using the inhomogeneous electrostatic and magnetic field is summarized. The typical experimental arrangements are presented, and some experimental results based on these techniques are reviewed. In addition, the theoretical representation to describe the effect of the mutual orientation of reagents on the outcome of reactive beam collisions is summarized. The axial distributions and the cross sections are expanded in series of Legendre polynomials and real spherical harmonics, respectively, and characterized by the expansion coefficients. The interrelations between the moments of the cross sections and the experimental data on the steric effect are presented.

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  One of the ultimate goals of surface science is to be able to design surfaces with particular catalytic reactivity. This entails a need for an atomic-level understanding of the fundamental principles (elementary processes) underlying the bond-making and bond-breaking at surfaces. It is expected that the orientation of an incoming molecule on the surface may play an important role in such elementary processes. We have been developing ultra-high-vacuum (UHV) oriented-molecular-beam machines in order to investigate for the initial molecular-orientation effects of an incoming molecule on the surface chemical processes. Oriented molecular beams demonstrate the possibility for controlling surface chemical reactions by varying the orientation of the incident molecules. The steric effects found on Si surfaces hint at new ways of material fabrication on Si surfaces.

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  Since most molecules are anisotropic quantum systems, alignment or orientation dependence called steric effects is ubiquitous nature in various phenomena where molecules are involved. Therefore, not only in stereodynamics of chemical reactions but also in electronic stereodynamics in molecules, alignment or orientation dependence is always a matter of central concern and the importance of molecular alignment and orientation techniques has been more and more rising. Here various molecular alignment and orientation techniques with intense nonresonant laser fields are reviewed mainly in chronological order. They include one- and three-dimensional molecular alignment both in the adiabatic regime and in the nonadiabatic regime, and one- and three-dimensional molecular orientation in the adiabatic regime. More recent progresses are the demonstrations of laser-field-free molecular orientation and all-optical molecular orientation. Finally future subjects and perspectives on the applications with a sample of aligned or oriented molecules are discussed.

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  Intense (10¹²-10¹³ W/cm²) phase-controlled laser fields consisting of a fundamental light and a second-harmonic light induce the directionally asymmetric tunneling ionization and the resultant selective ionization of oriented molecules. It is demonstrated that selective ionization of oriented molecules induced by phase-controlled ω+2ω laser fields reflects the geometric structure of the highest occupied molecular orbital. This method was robust, being free of both laser wavelength and pulse-duration constraints, and thus can be applied to a wide range of molecules.

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  O₂ is one of the most important chemical species in every field of natural science. In the present study, a state-selected triplet molecular oxygen beam, in which nearly 100% of the molecules are in the spin-rotational state of (J, M)=(2, 2), has been produced by combining a supersonic seeded O₂ beam with a hexapole magnet. The (2, −2) beam with >90% purity has also been obtained by a controlled non-adiabatic transition. The (2, ±2) beam, for which we can determine the spin and rotational angular momenta of O₂ almost independently, is the most promising probe for studying the spin effects as well as the steric effects in O₂ molecular scattering.

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  The thermal transpiration effect shown in intermediate flow and molecular flow regions influences the sensitivity of a capacitance diaphragm gauge (CDG) with a temperature controlled sensor head. This apparent change in the sensitivity of CDG owing to the thermal transpiration effect has to be compensated for precise pressure measurements in the range of lower than 150 Pa. In this study, the method and the uncertainty of the compensation are reported.
  Seven types of equations for the thermal transpiration effect were compared with the calibration results of high accuracy CDGs by the static expansion system. Takaishi-Sensui equation, Miller equation, and Setina equation show good agreement with the calibration results.
  The calibration results of CDGs also show that increasing the temperature of the vacuum chamber from 22.5°C to 26.0°C caused decreasing the sensitivity of CDGs by the thermal transpiration effect. The magnitude of the decrease in the sensitivity was from 0.09% for 10 Pa to 0.5% for 0.1 Pa.
  Such apparent changes in the sensitivity owing to the thermal transpiration effect could be compensated within 0.2% by Takaishi-Sensui equation using parameters quoted from the catalog and the literature values. In addition, this deviation could be reduced to less than 0.1% by fitting Takaishi-Sensui equation using the parameter c or the sensor temperature T₂.

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  The effects of high nitrogen (N₂) pressure and thermal treatment on the adhesion between a silicon film and a polyethersulfone (PES) substrate during crystallization by excimer laser annealing (ELA) were investigated using silicon nitride (SiN_x) as the barrier film for the fabrication of polycrystalline silicon (poly-Si) thin-film transistors on a plastic substrate. As the thickness of the SiN_x film increased from 50 to 150 nm at a gas pressure of 0.2 MPa, film exfoliation was suppressed. A poly-Si film with a crystalline fraction of 76% was obtained at an energy density of 200 mJ/cm² and a high pressure in N₂ atmosphere. In addition, thermal treatment before ELA was useful for improving the adhesion between the inorganic film and the PES substrate.

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