[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

An accurate description of the electrical properties of atoms and molecules is critical for quantitative predictions of the nonlinear properties of molecules and of long‐range atomic and molecular interactions between both neutral and charged species. We report a systematic study of the basis sets required to obtain accurate correlated values for the static dipole (α1), quadrupole (α2), and octopole (α3) polarizabilities and the hyperpolarizability (γ) of the rare gas atoms He, Ne, and Ar. Several methods of correlation treatment were examined, including various orders of Moller–Plesset perturbation theory (MP2, MP3, MP4), coupled‐cluster theory with and without perturbative treatment of triple excitations [CCSD, CCSD(T)], and singles and doubles configuration interaction (CISD). All of the basis sets considered here were constructed by adding even‐tempered sets of diffuse functions to the correlation consistent basis sets of Dunning and co‐workers. With multiply‐augmented sets we find that the electrical properties of the rare gas atoms converge smoothly to values that are in excellent agreement with the available experimental data and/or previously computed results. As a further test of the basis sets presented here, the dipole polarizabilities of the F− and Cl− anions and of the HCl and N2 molecules are also reported.

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Gaussian basis sets for use in correlated molecular calculations. IV. Calculation of static electrical response properties

A strategy for the design of molecules with large two-photon absorption cross sections, δ, was developed, on the basis of the concept that symmetric charge transfer, from the ends of a conjugated system to the middle, or vice versa, upon excitation is correlated to enhanced values of δ. Synthesized bis(styryl)benzene derivatives with donor-π-donor, donor-acceptor-donor, and acceptor-donor-acceptor structural motifs exhibit exceptionally large values of δ, up to about 400 times that of trans-stilbene. Quantum chemical calculations performed on these molecules indicate that substantial symmetric charge redistribution occurs upon excitation and provide δ values in good agreement with experimental values. The combination of large δ and high fluorescence quantum yield or triplet yield exhibited by molecules developed here offers potential for unprecedented brightness in two-photon fluorescent imaging or enhanced photosensitivity in two-photon sensitization, respectively.

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Design of Organic Molecules with Large Two-Photon Absorption Cross Sections

The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

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Optical gas sensing: a review

The non-linear optical polarization of an isolated atom or molecule is treated, giving careful consideration to secular and resonant terms in the perturbation expansion. The Method of Averages introduced by Bogoliubov and Mitropolsky is used. The case where resonance-induced excited state populations are negligible, which is relevant to a wide range of non-linear optical experiments, is examined in detail for polarizations through third order in the perturbing fields. This yields concise expressions which are valid for any combination of applied field frequencies, including static fields.

Perturbation theory of the non-linear optical polarization of an isolated system

Interferences due to easily ionised elements in a microwave-induced plasma system with graphite-furnace sample introduction

Discussion de plusieurs aspects de cette spectrometrie a haute resolution pour l'etude des transitions rovibroniques de C 2 H 2 , en particulier au niveau des transferts d'energie rotationnelle

Raman ultraviolet optical double resonance spectroscopy in gas phase acetylene

A pulsed beta-barium borate optical parametric oscillator is injection seeded by cw diode lasers, yielding continuously tunable narrow-band output at its idler wavelength. A notable feature of this optical parametric oscillator is that it comprises a simple passive ring cavity with no active control of path length as the seed wavelength is scanned. We demonstrate this by recording Doppler-limited photoacoustic absorption spectra of acetylene gas and Doppler-free two-photon fluorescence spectra of rubidium vapor.

Continuously tunable narrow-band operation of an injection-seeded ring-cavity optical parametric oscillator : spectroscopic applications

An injection-seeded optical parametric oscillator (OPO) based on periodically poled KTiOPO4 is pumped at 532 nm by relatively long (~27-ns) pulses from a specially constructed Nd:YAG laser. This pulsed OPO system generates continuously tunable, single-longitudinal-mode output at signal wavelengths near 842 nm, which is suitable for high-resolution spectroscopy. Optical-heterodyne measurements show that chirp in the instantaneous frequency of the pulsed OPO signal output radiation increases linearly as the seed frequency is detuned from the free-running (unseeded) OPO frequency. The frequency chirp can be maintained below 10 MHz, which is substantially less than the Fourier-transform-limited optical bandwidth (17.5 MHz full width at half-maximum for a 25-ns OPO signal pulse) and is insensitive to variation of the fluence of the pump radiation. The effects of detuning the OPO cavity length from resonance with the seed frequency and the onset of partially seeded OPO operation are also investigated.

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Control of frequency chirp in nanosecond-pulsed laser spectroscopy. 2. A long-pulse optical parametric oscillator for narrow optical bandwidth

A continuous-wave, rapidly swept cavity-ringdown spectroscopic technique has been developed for localized atmospheric sensing of trace gases at remote sites. It uses one or more passive open-path optical sensor units, coupled by optical fiber over distances of >1 km to a single transmitter/receiver console incorporating a photodetector and a swept-frequency diode laser tuned to molecule-specific near-infrared wavelengths. Ways to avoid interference from stimulated Brillouin scattering in long optical fibers have been devised. This rugged open-path system, deployable in agricultural, industrial, and natural atmospheric environments, is used to monitor ammonia in air. A noise-limited minimum detectable mixing ratio of ~11 ppbv is attained for ammonia in nitrogen at atmospheric pressure.

Brian J. Orr

Papers

Interferences due to easily ionised elements in a microwave-induced plasma system with graphite-furnace sample introduction

Raman ultraviolet optical double resonance spectroscopy in gas phase acetylene

Continuously tunable narrow-band operation of an injection-seeded ring-cavity optical parametric oscillator : spectroscopic applications

Control of frequency chirp in nanosecond-pulsed laser spectroscopy. 2. A long-pulse optical parametric oscillator for narrow optical bandwidth

Remote open-path cavity-ringdown spectroscopic sensing of trace gases in air, based on distributed passive sensors linked by km-long optical fibers.