bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fourier Transform Microwave Spectroscopy Measurement and Instrumentation
Authors: Grabow Jens‐Uwe 
Published: September 2011

AbstractMicrowavemolecular spectroscopy is progressing impressively. In part, profiting from recent experimental developments that combine jet‐expansion sources with elaborate means for preparation of new chemical systems, advances in spectroscopic instrumentation — namely, the rise of very sensitive and high‐resolution time‐domain techniques — are even more significant. Precise structural studies have always been a strength of rotational spectroscopy; now problems arising from convoluted intramolecular dynamics, such as conformational, tautomeric equilibria, and other large amplitude motions, as well as intermolecular vibrational energy redistribution and isomerization, can be targeted with the unrivaled precision of rotational investigations. Numerous interesting chemical systems like molecules with multiple concurrent internal motions, larger complexes, aggregates, biomolecules, and transient species were characterized recently — positioning microwave spectroscopy today as a prime method for the investigation of multidimensional flexible systems. Rotational studies elucidate an extensive range of intermolecular interactions, ranging from hydrogen bonding and van der Waals interaction to the unusual effects observed in quantum solvation. The development of microwave pulsed excitation multiresonance techniques and the advent of instantaneous broadband‐coverage microwave spectroscopy are impressively boosting the capabilities of rotational spectroscopy to quite routinely disentangle the unique spectral signatures that encode the structure and dynamics of hitherto pathological molecular cases. The versatile capabilities of microwave coherence spectroscopy are outlined in the treatment of time‐dependent interaction of rotating molecules with radiation.
Millimeter and Submillimeter Wave Spectroscopy and Astrophysical Applications
Authors: Ziurys Lucy M. 
Published: September 2011

AbstractMillimeter and submillimeter spectroscopy has played a crucial role in the discovery and study of interstellar molecules by radio astronomy, as well as in the characterization of the rotational energy levels for numerous chemical compounds. A broad range of spectrometer designs have been developed for this basic direct absorption technique. Certain systems employ “free space” cells and Gaussian beam optics, while others incorporate mirrors in multipass configurations. Fast scanning methods have additionally been implemented. Synthetic techniques are also important in the astrophysical application of millimeter/submillimeter spectroscopy, as many potential interstellar species are free radicals and molecular ions. Many instruments employ glow discharges, ovens, and other exotic gas‐phase methods for the creation of transient molecules. Radical spectra usually exhibit a range of fine structure and hyperfine interactions which can complicate their analysis. Another challenge for millimeter/submillimeter spectroscopy is the study of simple organic molecules with functional groups that undergo hindered rotation. Millimeter and submillimeter spectroscopic measurements continue to provide the necessary rotational “rest frequencies” for molecule identification in space. Recent work has led to the interstellar discoveries of long‐chain carbon anions C4H−and C6H−, more complex organic molecules including CH3CONH2, and unusual refractory species such as CCP and AlO.
High‐Resolution Fourier Transform Infrared Spectroscopy
Authors: Albert Sieghard , Albert Karen Keppler , Quack Martin 
Published: September 2011

AbstractRecent developments and applications of high‐resolution Fourier transform spectroscopy are reviewed. A short historical summary of the development of high‐resolution interferometric Fourier transform infrared (FTIR) spectrometers is given and the possibilities of the currently most highly resolving FTIR spectrometers, including a current prototype built for the Zürich group at the Swiss Light Source SLS as a synchrotron light source, are discussed. A short description of the principles of FTIR spectroscopy is given and the resolution of current spectrometers is illustrated by FTIR spectra of CO, CO2OCS, N2O, CS2, and CH4and its isotopomers. The computational tools necessary to analyze FTIR spectra are described briefly. As examples of rovibrational analysis of more complex spectra, selected molecules CHCl2F, CDBrClF, pyridine (C6H5N) and pyrimidine (C4H4N2), and naphthalene (C10H8) are discussed. The spectrum of CHCl2F, a fluorochlorocarbon, is of interest for a better understanding of the chemistry of the Earth's atmosphere. It also possesses an isotopically chiral isotopomer CH35Cl37ClF analyzed in natural abundance. CDBrClF is a chiral molecule and therefore the analysis of its rovibrational spectra provides the basis for carrying out further experiments toward the detection of molecular parity violation. The analyses of the pyridine, pyrimidine, and naphthalene FTIR spectra illustrate the potential of the new generation of FTIR spectrometers in the study of spectra and rovibrational dynamics of aromatic systems and molecules of potential biological interest. In particular, naphthalene is a prototype molecule useful in gaining an understanding of the unidentified infrared bands (UIBs) detected in several interstellar objects.
High‐resolution Infrared Laser Spectroscopy and Gas Sensing Applications
Authors: Sigrist Markus W. 
Published: September 2011

AbstractThe acceptance and the success of laser‐based trace gas sensing techniques crucially depend on the availability and performance of tunable laser sources combined with appropriate detection schemes. Near‐ and midinfrared sources (preferentially semiconductor and solid state lasers) are used today in various configurations with sensitive absorption detection methods (multipass, photoacoustic, and cavity ringdown arrangements). This article starts with a discussion of the approaches pursued to fulfill key requirements for gas sensors. In the main part, we present the challenges, performance, potential, and also limitations of laser‐based sensors in various applications. The examples cover ambient air monitoring, industrial sensing, isotope ratio determination, breath analysis in medical diagnosis, and finally analysis of urine samples for doping tests. Besides multicomponent capability, impressive sensitivities down to the parts per trillion level (1 in 1012), high specificity which enables differentiation between diastereoisomers (e.g., between ephedrine and pseudoephedrine, even in urine samples) or between isotopes (14N15N16O and15 N14 N16O, site selectivity), are dealt with. We describe both ground‐based and airborne instruments for time‐resolved measurements. Promising developments are expected to foster further progress of laser‐based sensors and stimulate their application in new areas.
High‐resolutionRaman Spectroscopy of Gases
Authors: Weber Alfons 
Published: September 2011

AbstractA review of high‐resolution Raman spectroscopy of gases, including spontaneous, incoherent Raman spectroscopy, as well as of nonlinear techniques for coherent anti‐Stokes scattering (CARS), stimulated Raman gain (SRG) and stimulated Raman loss (SRL) spectroscopy, and photoacoustic Raman spectroscopy (PARS) in the frequency domain is presented. Femtosecond degenerate four‐wave mixing spectroscopy (Fs‐DFWM) and Raman‐induced polarization spectroscopy (RIPS) in the time domain are discussed. Also treated are the broadenings of Raman lines due to the Doppler and pressure effects. Basic theoretical notions and working equations for the analysis of highly resolved spectra are presented. Examples are drawn from the literature to illustrate the respective advantages and disadvantages of the various techniques. The interplay between high‐resolution Raman spectroscopy, infrared spectroscopy, and ab initio computational schemes is illustrated. The article concludes with an overall assessment of the respective advantages and disadvantages of the methods used in high‐resolution Raman spectroscopy.
Mass and Isotope‐Selective Infrared Spectroscopy
Authors: Hippler Michael , Miloglyadov Eduard , Quack Martin , Seyfang Georg 
Published: September 2011

AbstractRecent advances in laser spectroscopic techniques make it possible to obtain mass‐ and isotope‐selective infrared spectra of gas‐phase species at high resolution and reduced hot‐band spectral congestion. In these techniques, infrared excitation is coupled with ultraviolet multiphoton ionization and detection of the resulting ions in a mass spectrometer, which allows the separation of contributions of different isotopomers and, more generally, species of different mass in a mixture. In combination with jet cooling techniques, spectra are obtained for very cold molecules. These spectra can then be analyzed to extract information on dynamical processes such as intramolecular vibrational redistribution or tunneling and rearrangement processes, and on how intramolecular dynamics is influenced by vibrational excitation and isotope effects. In this review, we introduce isotope‐selective infrared spectroscopic techniques and present some selected applications on isotope effects and intramolecular dynamics of vibrationally excited chloroform, aniline, and benzene obtained by isotope‐selective infrared spectroscopy.
Electronic Spectroscopy of Transient Molecules
Authors: Guennoun Zohra , Maier John P. 
Published: September 2011

AbstractThe generation and characterization of transient species is a challenge for experimentalists as these species are short‐lived and reactive. Our group has focused on the measurement of the electronic spectra of unstable molecules relevant to astrophysical observations as well as to terrestrial environments. Methods of generating and collecting the electronic spectra of radicals and ions have been developed. By first using a mass‐selected matrix isolation technique, the transitions of these species are obtained in neon matrices, following which the gas‐phase transitions can be sought. To this end, an assortment of techniques is employed, for example, cavity ring‐down and frequency modulation absorption spectroscopy, degenerate four‐wave mixing, resonant multiphoton ionization, and photofragmentation schemes that utilize the cooling capabilities of an ion trap.These gas‐phase‐based approaches are illustrated by the electronic spectra of a number of key species providing detailed information about their electronic structure, thus allowing for direct comparison between astronomical observations and theory. The studies of the carbon chains have led to interesting astrophysical implications for the systems, which could be responsible for the diffuse interstellar bands.
High‐resolution RotationalRaman Coherence Spectroscopy with Femtosecond Pulses
Authors: Frey Hans‐Martin , Kummli Dominique , Lobsiger Simon , Leutwyler Samuel 
Published: September 2011

AbstractFemtosecond time‐resolved rotational coherence spectroscopy (RCS), when applied in a Raman scattering version, can be utilized for the measurement of highly accurate rotational and centrifugal constants of ground and vibrationally excited states of nonpolar molecules. A brief outline of the theoretical background is given, including the basics of rotational coherence spectroscopy, nonlinear optical four‐wave mixing (FWM), molecular polarizability, the rotational Raman process, nuclear spin statistics, and collisional dephasing. An experimental setup for femtosecond rotational Raman RCS measurements is described, featuring some of the points necessary to achieve high experimental accuracy. Rotational Raman RCS spectroscopy has been performed on a number of nonpolar linear and symmetric‐top molecules. The examples presented here (CS2, cyclobutane, and cyclooctatetraene) are selected to show the scope of the method and currently achievable accuracy of the rotational and the centrifugal distortion constants, as well as the detailed considerations necessary to achieve these results. The last section reviews a procedure for the determination of semiexperimental equilibrium structures.
Theory of the Jahn–Teller Effect
Authors: Köppel Horst , Cederbaum Lorenz S. , Mahapatra Susanta 
Published: September 2011

AbstractAn overview of theoretical treatments of Jahn–Teller (JT) and pseudo‐Jahn–Teller (PJT) coupling effects involving doubly degenerate electronic states is presented. It is divided into a general part, focusing on the pertinent Hamiltonians and the properties of the adiabatic potential energy surfaces, and the presentation of specific examples, where the consequences for molecular electronic spectra are demonstrated. Besides isolatedEelectronic states with various types and symmetries of the JT‐active modes, interactions between degenerate and nondegenerate as well as between different degenerate states are also covered. The examples are dominated by strong nonadiabatic coupling effects that are caused by the various conical intersections appearing in these systems. The similar nature of JT and PJT intersections in this respect is pointed out.
Effective Hamiltonians for Electronic Fine Structure and Polyatomic Vibrations
Authors: Field Robert W. , Baraban Joshua H. , Lipoff Samuel H. , Beck Annelise R. 
Published: September 2011

AbstractThe effective Hamiltonian,Heff, is an important tool for analyzing and representing the spectra, energy levels, and dynamics of atoms and molecules. By replacing the rigorous but intractable exact Hamiltonian,Hexact, with a model that is designed to share most of its essential qualitative and quantitative characteristics, the spectroscopist can derive valuable insights from raw, incomplete, and partially assigned spectra. These insights guide the optimal design of information‐rich new experiments and computations and can reveal the dynamical mechanisms encoded in the spectra. Here we describe the theory, construction, and limitations of effective Hamiltonians, drawing examples primarily from the electronic fine structure of diatomic molecules and the vibrational structure of polyatomic molecules. Current ideas for extending the accuracy, flexibility, and mechanistic transparency of effective Hamiltonian models to future areas of research, especially at extremely high excitation energies, are discussed. Unconventional applications of traditional effective Hamiltonians are illustrated by example, especially schemes to visualize and classify large‐amplitude motions. Quantum and classical mechanicalHeffmodels derived from frequency‐domain spectra are the best possible sources for insights into time‐domain phenomena. In particular, the existence of large‐amplitude regular eigenstates embedded in a principally ergodic bath is uniquely relevant to schemes for external control of intramolecular dynamics and the validity of ergodicity‐based predictions of the rates of unimolecular processes.
Helium Droplets as Nanocryostats for Molecular Spectroscopy—from the Vacuum Ultraviolet to the Microwave Regime
Authors: Callegari Carlo , Ernst Wolfgang E. 
Published: September 2011

AbstractThe spectroscopy of pure and doped helium nanodroplets is reviewed, with the goal to provide a reference for nonspecialists. The technical aspects of a helium‐droplet machine for spectroscopy are addressed first. Spectroscopic methods and results are then presented, loosely divided according to the degree of freedom being excited (that is, practically, by photon energy). Technical aspects pertaining to each branch are presented, along with an overview of the physics that can be studied and of possible physical‐chemistry applications. References for further reading are provided.
Molecular Clusters and Noncovalent Bonds Probed by Photoionization and Photoelectron Spectroscopy
Authors: Müller‐Dethlefs Klaus , Riese Mikko 
Published: September 2011

AbstractThis article gives a brief impression of how high‐resolution photoion and photoelectron spectroscopy can be applied to investigate molecular clusters. A short theoretical description of the nature of noncovalent interactions is given. In this context, we discuss which properties can best be investigated by applying a variety of spectroscopic techniques. The principles of the main photoion/photoelectron spectroscopy techniques are explained and examples of investigations of molecular clusters are presented. Van der Waals (vdW) clusters that are composed of a molecule and one or more rare‐gas atoms as well as hydrogen‐bonded hetero dimers are discussed. Complexes containing aniline or phenol are interesting because of two principal ligand binding sites, thus allowing either hydrogen bonding via the NH2or OH group (H‐bound) and vdW bonding via interaction with the aromatic π system (π‐bound). For phenol…Arnand aniline…Arn(n = 1, 2), we discuss the very recently observed phenomenon of π→ H isomerization in the cation cluster. The interplay between different types of intermolecular bonds during fragmentation is discussed for the example of phenol…water…argon. For the fluorobenzene…Ar cluster, we demonstrate how structural information from rotational constants for the ionic state can be obtained from partially rotational‐resolved zero‐electron kinetic energy (ZEKE) spectra.
Spectroscopy and Reaction Dynamics of Anions
Authors: Wester Roland 
Published: September 2011

Abstract
This article covers the status and the recent advances in experimental studies on the spectroscopy and the dynamics of negative ions. Bound–bound absorption spectroscopy in the different frequency ranges as well as bound‐free photodetachment and photoelectron spectroscopy of anions are discussed. Furthermore, recent developments in the field of reaction kinetics and dynamics of negative ions are presented.
High‐resolution Photoelectron Spectroscopy
Authors: Merkt Frédéric , Willitsch Stefan , Hollenstein Urs 
Published: September 2011

AbstractThe evolution of photoelectron spectroscopy of neutral molecules in the gas phase, from its first applications in the early 1960s to the present day, is reviewed with emphasis on the description of methods that have contributed to the improvement of resolution. In the early days, photoelectron spectroscopy was very successfully used to study the electronic structure of molecules. As the resolution improved, the emphasis gradually shifted to studies of the structure and dynamics of molecular cations. Current methods enable one to fully resolve the rotational structure in the photoelectron spectra of polyatomic molecules and even to measure the fine and hyperfine structures of positively charged atoms and small molecules. Several of the methods providing high resolution make use of the long lifetimes and electric‐field‐ionization properties of high Rydberg states and give access to detailed information on molecular ionization channels and molecular photoionization.
Precision Laser Spectroscopy in the Extreme Ultraviolet
Authors: Eikema Kjeld S.E. , Ubachs Wim 
Published: September 2011

AbstractTechniques for the production of short wavelengths in the extreme ultraviolet wavelength range are described, spanning low‐order harmonic generation in the perturbative regime for narrow bandwidth XUV production to the plateau‐regime with the three‐step collisional model for the generation of high harmonics with broadband ultrafast pulses. In addition, the intermediate regime is discussed for pulses of 300 ps duration, as well as the regime of harmonic conversion based on continuous wave lasers aiming at the production of coherent Lyman‐α radiation. Applications of XUV sources in the frequency domain typically rely on the production of XUV‐light from narrowband Fourier‐transform‐limited pulses for recording high‐resolution spectra. Alternatively, harmonically upconverted pulses of ultrashort duration (with inter‐pulse coherence) can be used for spectroscopic studies in the time and frequency domain (such as direct frequency comb spectroscopy techniques). Examples of both approaches for atomic and molecular spectroscopy are discussed at some length. For precision metrology on atomic systems, a focus is put on the Lamb shift determination in the He ground state. In the realm of molecular spectroscopy, predissociation phenomena in the nitrogen molecule are highlighted, with relevance for dissociation processes occurring in the upper layers of the Earth atmosphere. Similar predissociation phenomena in carbon monoxide are also treated in some detail, in this case with relevance for the chemistry in interstellar clouds. Precision XUV spectroscopy of molecular hydrogen is discussed as well, as it relates to the possibility of detecting a variation of the proton–electron mass ratio on a cosmological time scale. In the last section, applications of direct frequency comb spectroscopic techniques at short wavelengths are explained and prospects are given for using these techniques at extreme ultraviolet wavelengths.
Femtosecond and Attosecond Light Sources and Techniques for Spectroscopy
Authors: Gallmann Lukas , Keller Ursula 
Published: September 2011

AbstractThe quest for high‐resolution time‐resolved studies of ultrafast physical and chemical processes is an important driver behind ultrafast laser technology. The large variety of physical and chemical systems leads to the need of ultrashort laser pulses at many different wavelengths. In this article, we review the most important femtosecond and attosecond light sources available from the infrared to the X‐ray spectral region and give an introduction to the underlying physics and technology. We discuss techniques for ultrashort pulse diagnostics, which can be considered as prototypes for time‐resolved experiments in the femtosecond and attosecond domain. The topics covered in this article are intended as a starting ground and the interested reader is provided with references for further exploration.
Photodissociation Dynamics of Polyatomic Molecules: Diffuse Structures and Nonadiabatic Coupling
Authors: Schinke Reinhard 
Published: September 2011

AbstractThe photodissociation of polyatomic molecules is discussed in terms of accurate potential energy surfaces for excited electronic states and exact quantum mechanical dynamics calculations. After a brief presentation of the theoretical tools, diffuse vibrational structures are discussed in detail for several triatomic molecules in order to elucidate the relationship with the intramolecular dynamics in excited states. Another focus is the various types of nonadiabatic transitions between different states along the dissociation path.
Multiphoton Resonance Spectroscopy of Biological Molecules
Authors: Häber Thomas , Kleinermanns Karl 
Published: September 2011

Abstract
High‐resolution gas‐phase spectroscopy of biomolecules allows us to distinguish between the intrinsic properties of biomolecules and those properties that are induced by solvation or by the geometrical restrictions of the environment. In the gas phase, we can study the isolated biomolecules and their water clusters under size‐controlled conditions. Comparison with experiments in solution then provides information about the specific role of the biological environment, like solvent effects or geometric constraints of nucleic acids and peptides. However, gas‐phase studies are often complicated by the thermal instability of many biomolecules, which often prevents the use of conventional thermal sources for vaporizing them. This obstacle has been overcome by applying laser desorption techniques to biomolecules as a gentle alternative to thermal heating in combination with very sensitive detection schemes like resonance‐enhanced multiphoton ionization, double resonance methods, and dispersed fluorescence.