微波波谱方法与应用研究进展

综述了微波波谱法及其应用研究进展,阐述了微波波谱法的基本原理及仪器构造。对微波波谱法在分子结构及构象分析、弱相互作用体系的研究、分析化学、星际物质的探测等方面的应用进行了综述。并展望了微波波谱方法未来的发展趋势。     

微波波谱技术和应用*

微波波谱法具有研究分子系统的结构、构象平衡、分子间相互作用、分子内部运动等物理化学动力学过程的能力。本文综述了微波波谱技术的进展。对微波吸收波谱仪、脉冲喷嘴傅立叶变换微波波谱仪、线性脉冲傅立叶变换微波波谱仪等技术进展进行了论述,详细介绍了脉冲喷嘴阀技术、外部场调制、微波二次共振、线性脉冲、快速扫描等技术,分析了微波谱仪在分析测试领域的发展。对微波谱仪的未来发展做了展望。     

微波波谱法研究水与有机/生物分子的分子配合物

微波波谱法是一种高灵敏度、高分辨率的研究分子系统内部动力学及超精细结构的方法,能解决许多其他方法难以解决的化学与物理领域具有挑战性的难题。本文综述了微波波谱法研究水分子与有机或生物分子形成分子配合物的内部动力学过程,详细讨论了不同类型的有机或生物分子与水分子形成的分子配合物,介绍了水在分子配合物中作为质子给体和质子受体的动力学,形成分子配合物后水分子和配体分子的隧道运动、结构和构象变化等动力学过程,并讨论了分子配合物中水分子和有机或生物分子的内部运动、相互作用键的强度、对称性影响隧道动力学特性。最后,展望了微波波谱法的发展方向。     

微波波谱法研究分子系统内基团大幅度运动动力学

分子中基团的运动方式、机制对分子体系性质、分子功能的表达等具有重要作用。微波波谱法在研究分子系统内部动力学、分子结构、构象变化、弱相互作用、基团大幅度运动以及探索量子溶剂等方面具有独特的能力,特别适合研究分子的精细结构、分子系统基团的内部转动运动,具有高灵敏度、高分辨率的特点。本文讨论了微波波谱法在研究分子系统基团大幅度运动动力学方面的应用,包括分子系统中甲基基团的内部转动、OH基团的运动、氨和氨基化合物的反演以及环状有机分子环运动等的动力学,同时结合作者使用微波波谱法研究的部分体系进行了分析。     

星际化学简介

近十多年来,在射电天文学、空间科学、环境保护学等学科的推动下,星际化学有了引人注目的发展。星际化学,以天文学同化学的结合为特征,主要研究星际云中分子的生成与转化,考察离子-分子反应对非地球环境中有机分子     

星际分子

六十年代在星际空间发现了比较复杂的星际分子,作为六十年代天文学四大发现而载入史册,七十年代已发现星际分子的数目与日俱增,到目前共发现60几种。随着星际分子不断发现,天文学开拓了“分子天文学”的新领域,     

超临界水理论研究的进展*

通过计算模拟、拉曼光谱、NMR以及衍射分析对超临界水静态结构进行了广泛的研究,氢键结构是这些研究的重要内容。研究结果显示在临界点附近水的氢键结构受到很大的破坏,只有相当于常温下29％左右的氢键存在。利用微波波谱法、NMR法以及准弹性不边疆中子散射方法对超临界水动力学进行了研究。结果发现,在临界点附近,水分子的动力学重排时间急剧缩短,这就使得以超临界水为介质的化学反应速率大大增加。由于微波的周期比较长,可能大大地超过了超临界水结构的动力学重排时间,因此微波波谱法不适合于高温低密度超临界水的动力学研究。今后需要加强超临界水氢键结构变化的机理和动力学的实验与模拟的研究。     

某些导电高分子的波谱性能

本文以聚吡咯和聚噻吩为例，对导电高分子的紫外－可见光谱、红外光谱、远红外及微波区的波谱性能进行了综述，并分析了波谱性能与结构的关系。对导电高分子波谱性能的实际应用前景也进行了论述。     

微波辅助有机合成中“非热效应”的研究方法

微波作为一种新颖的加热方式,极大地提高了有机合成的效率.对于微波促进有机合成反应机理,人们提出了它具有"非热效应".本文从微波对分子的影响、微波光量子对化学键的影响以及微波对化学反应的影响3个方面,对"非热效应"存在的理论依据进行了阐述;从理论、实验以及两者相结合的角度,对"非热效应"的研究方法与技术进行了综述.     

在星际媒介中合成H2NCH2CN分子的理论研究

在早期地球原始化学生命起源过程中, 氨基酸是重要的必需的生物化合物, 生成肽和蛋白. 为了探究一个可能的新的氨基酸起源, 采用密度泛函理论(B3LYP)在6-311++G(d, p) 基组水平上研究了在星际媒介条件下在气相中和在模拟的冰颗粒表面上的化学反应: CH2NH分子和两个异构体分子HNC/HCN通过Strecker合成生成H2NCH2CN(氨基乙氰, 一个重要的苷氨基酸前置分子). 在研究体系中, CH2NH、HCN、HNC 和H2O分子存在于星际密集分子云中, 且早于地球广泛存在. 研究证明, 这些分子之间在星际媒介条件下和在冰颗粒表面上通过Strecker合成路线很容易生成H2NCH2CN. 所以, H2NCH2CN分子在宇宙的星际密集分子云中是广泛存在的. 还讨论了H2NCH2CN分子在新的氨基酸起源中所起的作用, 以及在通过“原始汤”生命起源理论解析早期地球生命起源中可能所起的作用.     

Early events and some later developments in microwave spectroscopy

The early history of microwave spectroscopy is reviewed. New directions in the field are indicated. These include: further extensions of coherent submillimeter wave spectroscopy, microwave spectroscopy of molecules in interstellar space, microwave-infrared laser double resonance, spectroscopy of ionized molecules and transient molecular radicals, studies of hydrogen-bonded molecular complexes and atom-molecule complexes, observations of “forbidden” rotational transitions in symmetric-top and spherical-top molecules, and new developments in high-temperature spectroscopy.     

Dynamics of small,floppy molecules studied by high-resolution spectroscopic techniques

In molecular spectroscopy one of the common interests is how to transform the information obtained by high-resolution spectroscopic techniques into some reliable approximation of the potential energy surface of a particular molecule. Traditionally vibrational spectroscopy has been used. Rotational spectroscopy can only probe, at least at room temperature, molecular transitions arising from excited vibrational states up to approximately 1000 cm^?1. This corresponds roughly to 10% of a typical bond dissociation energy. However, floppy molecules which exhibit a large-amplitude, low-lying vibrational mode can be studied to a large extent by rotational spectroscopy in the microwave, millimeter and submillimeter wave range. Quasilinearity is a special form of large-amplitude motion, which complicates the observed molecular spectra substantially and which presents a real challenge to theoretical spectroscopists. In this lecture the highlights of quasilinear behavior of the molecules HCNO, OCCCO, HNCS and HNCO will be discussed. Another form of large amplitude motion is the inversion exhibited primarily by molecules derived from NH₃. Isocyanamide will be discussed and its special spectroscopic features will be shown. Cyanamide and isocyanamide are potential prebiotic molecules: cyanamide has been detected as a constituent in the interstellar medium. The analysis of the molecular dynamics of these molecules is shown to be necessary for understanding the frequencies and intensities of the observed spectra in the laboratory and in interstellar space.     

Carbon chains and rings in the laboratory and in space

Seventy-seven reactive organic molecules of astrophysical interest have been identified in a supersonic molecular beam, 73 in the radio band by Fourier-transform microwave spectroscopy, four in the optical by laser cavity ringdown spectroscopy. Most are linear carbon chains, but six consist of carbon chains attached to the compact, highly polar C3 ring, and two are rhomboidal cyclic configurations of SiC3. The laboratory astrophysics of the radio molecules is complete for the time being, in the sense that essentially all the rotational transitions of current interest to radio astronomy (including hyperfine structure when present) can now be calculated to a small fraction of 1 km s(-1) in equivalent radial velocity; six of the radio molecules have already been detected in space on the basis of the present data. The FTM spectrometer employed in this work is far from fundamental limits of sensitivity, so many more molecules can probably be found by refinements of present techniques. The density of reactive molecules in our supersonic beam is generally high by the standards of laser spectroscopy, and many of the radio molecules probably have detectable optical transitions which we are attempting to find, largely motivated by the long-standing problem of the diffuse interstellar bands. Our most interesting result to date is the detection of a fairly strong molecular band at 443 nm in a benzene discharge, in exact coincidence with the strongest and best known interstellar band. Isotopic shifts measured with partially and totally deuterated benzene suggest that the carrier of the laboratory band is a hydrocarbon molecule with the elemental formula CnH5, with n most likely in the range 3-6.     

Searches for new interstellar molecules, including a tentative detection of aziridine and a possible detection of propenal

Rotational spectroscopy at millimeter wavelengths is a powerful means of investigating the chemistry of dense interstellar clouds. These regions can exhibit an interesting complement of gas phase molecules, including relatively complex organics. Here we report the tentative first astronomical detection of aziridine (ethylenimine), the possible detection of propenal (acrolein), and upper limits on the abundances of cyclopropenone, furan, hydroxyethanal (glycolaldehyde), thiohydroxylamine (NH2SH), and ethenol (vinyl alcohol) in various interstellar clouds.     

Interstellar chemistry: a strategy for detecting polycyclic aromatic hydrocarbons in space

Polycyclic aromatic hydrocarbons (PAHs) have long been postulated as constituents of the interstellar gas and circumstellar disks. Observational infrared emission spectra have been plausibly interpreted in support of this hypothesis, but the small (or zero) dipole moments of planar, unsubstituted PAHs preclude their definitive radio astronomical identification. Polar PAHs, such as corannulene, thus represent important targets for radio astronomy because they offer the possibilities of confirming the existence of PAHs in space and revealing new insight into the chemistry of the interstellar medium. Toward this objective, the high-resolution rotational spectrum of corannulene has been obtained by Fourier transform microwave spectroscopy, and the dipole moment (2.07 D) of this exceptionally polar PAH has been measured by exploiting the Stark effect.     

Efficient surface formation route of interstellar hydroxylamine through NO hydrogenation. I. The submonolayer regime on interstellar relevant substrates

Dust grains in the interstellar medium are known to serve as the first chemical laboratory where the rich inventory of interstellar molecules are synthesized. Here we present a study of the formation of hydroxylamine-NH(2)OH-via the non-energetic route NO + H (D) on crystalline H(2)O and amorphous silicate under conditions relevant to interstellar dense clouds. Formation of nitrous oxide (N(2)O) and water (H(2)O, D(2)O) is also observed and the reaction network is discussed. Hydroxylamine and water results are detected in temperature-programmed desorption (TPD) experiments, while N(2)O is detected by both reflection-absorption IR spectroscopy and TPD techniques. The solid state NO + H reaction channel proves to be a very efficient pathway to NH(2)OH formation in space and may be a potential starting point for prebiotic species in dark interstellar clouds. The present findings are an important step forward in understanding the inclusion of interstellar nitrogen into a non-volatile aminated species since NH(2)OH provides a solid state nitrogen reservoir along the whole evolutionary process of interstellar ices from dark clouds to planetary systems.     

Microwave spectra and molecular structures of (Z)-pent-2-en-4-ynenitrile and maleonitrile.

Accurate equilibrium structures have been determined for (Z)-pent-2-en-4-ynenitrile (8) and maleonitrile (9) by combining microwave spectroscopy data and ab initio quantum chemistry calculations. The microwave spectra of 10 isotopomers of 8 and 5 isotopomers of 9 were obtained using a pulsed nozzle Fourier transform microwave spectrometer. The ground-state rotational constants were adjusted for vibration-rotation interaction effects calculated from force fields obtained from ab initio calculations. The resultant equilibrium rotational constants were used to determine structures that are in very good agreement with those obtained from high-level ab initio calculations (CCSD(T)/cc-pVTZ). The geometric parameters in 8 and 9 are very similar; they also do not differ significantly from the all-carbon analogue, (Z)-hex-3-ene-1,5-diyne (7), the parent molecule for the Bergman cyclization. A small deviation from linearity about the alkyne and cyano linkages is observed for 7-9 and several related species where accurate equilibrium parameters are available. The data on 7-9 should be of interest to radioastronomy and may provide insights on the formation and interstellar chemistry of unsaturated species such as the cyanopolyynes.     

Spectroscopy among the stars

The space between the stars is not void, but filled with interstellar matter, mainly composed of dust and gas, which gather in large interstellar clouds. In our Galaxy these interstellar clouds are distributed along a thin, but extended layer which basically traces out the spiral distribution of matter: the stars, the gas, and the dust component. Up to the present time more than 100 different molecules have been identified in interstellar molecular clouds. The majority of the interstellar molecules constitute carbon containing organic substances. During the past years, overwhelming evidence has been gathered, mainly through spectroscopic observations, that interstellar molecular clouds provide the birthplaces for stars. In fact detailed high spectral and spatial resolution spectroscopic measurements reveal physical and chemical processes of the intricate star formation process.