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Generalized perspective on chiral measurements without magnetic interactions
摘要： We present a unified description of several methods of chiral discrimination based exclusively on electric-dipole interactions. It includes photoelectron circular dichroism (PECD), enantiosensitive microwave spectroscopy (EMWS), photoexcitation circular dichroism (PXCD), and photoelectron-photoexcitation circular dichroism (PXECD). We show that, in spite of the fact that the physics underlying the appearance of a chiral response is very different in all these methods, the enantiosensitive and dichroic observable in all cases has a unique form. It is a polar vector given by the product of (i) a molecular pseudoscalar and (ii) a field pseudovector specified by the configuration of the electric fields interacting with the isotropic ensemble of chiral molecules. The molecular pseudoscalar is a rotationally invariant property, which is composed from different molecule-specific vectors and in the simplest case is a triple product of such vectors. The key property that enables the chiral response is the noncoplanarity of the vectors forming such triple product. The key property that enables chiral detection without relying on the chirality of the electromagnetic fields is the vectorial nature of the enantiosensitive observable. Our compact and general expression for this observable shows what ultimately determines the efficiency of the chiral signal and if, or when, it can reach 100%. We also discuss the differences between the two phenomena, which rely on the bound states, PXCD and EMWS, and the two phenomena using the continuum states, PECD and PXECD. Finally, we extend these methods to arbitrary polarizations of the electric fields used to induce and probe the chiral response.
关键词： photoelectron-photoexcitation circular dichroism,electric-dipole interactions,field pseudovector,enantiosensitive microwave spectroscopy,photoexcitation circular dichroism,molecular pseudoscalar,chiral discrimination,photoelectron circular dichroism
更新于2025-09-23 15:23:52
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Frequency Extension of Atomic Measurement of Microwave Strength Using Zeeman Effect
摘要： Measuring the field strength of an electromagnetic wave based on atomic quantum mechanics is expected to be an innovative method to realize stable and reliable measurements. However, the major issue of atomic measurements is that the measurable frequency is limited to the resonant frequency of atoms. Therefore, in this paper, we demonstrate the measurement at arbitrary frequencies using the Zeeman effect in a static magnetic field. A cesium vapor cell is placed in a static magnetic field of approximately 40 mT, which causes the resonant frequency of the cesium atom to shift from 9.2 to 8.2 GHz. In addition, the Rabi frequency due to the interaction between cesium atoms and microwaves is measured at the frequency of 8.2 GHz in this experiment.
关键词： frequency measurement,microwave measurements,metrology,microwave spectroscopy,electromagnetic measurements,Atom optics,atomic measurements,measurement standards
更新于2025-09-23 15:22:29
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Mapping corrosion with hyperspectral imaging
摘要： Hydrogen bonds are one reason for water’s unique boiling and freezing behavior and other properties. But scientists have debated for decades whether dimers of hydrogen sulfide, water’s smelly triatomic cousin, also sport hydrogen bonds. Now, Elangannan Arunan of the Indian Institute of Science and colleagues report they have found experimental evidence that hydrogen bonds do indeed hold H2S dimers together. Water’s four hydrogen bonds (via two H atoms and two lone electron pairs) are evident in ice’s tetrahedral structure, but in solid H2S, each molecule is surrounded instead by a shell of 12 others. That suggested to some that H2S does not hydrogen bond. Using microwave spectroscopy, Arunan’s group detected rotational energy barriers in the dimer below about 60 °C that they say indicate the presence of hydrogen bonds. Computational chemists have reached the same conclusion. Arunan explains that at higher temperatures, those bonds break and re-form too quickly to be detected via spectroscopy. He adds that the observation that the distance between the H and S atoms is smaller than their combined van der Waals radii and that the S–H–S angle is nearly 180° further confirms hydrogen bonding.
关键词： computational chemistry,microwave spectroscopy,Hydrogen bonds,H2S dimer
更新于2025-09-09 09:28:46