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During the last years there has been a rapidly growing interest in the field of cold molecules. This has obviously been inspired by the spectacular successes in the closely related field of cold atoms, which have recently been recognized by the award of the 2001 Nobel Prize in Physics to Cornell, Ketterle, and Wieman. But molecules have much more to offer than simply extending the experiments already performed with atoms to more complex species.

Cavity ring down absorption spectroscopy with a continuous light source is used to measure the transition frequencies and absolute absorption coefficient of the weak b1Σg+(v′ = 2) ← X 3Σg−(v″ = 0) transition of 18O2. The absorption spectrum is extracted from a measurement of the magnitude of the phase shift that an intensity modulated continuous light beam experiences upon passing through an unstabilized optical cavity.

A compact diode laser operating around 1.5 mum was used to measure cavity enhanced absorption spectra of hot water molecules and OH radicals in radiative environments under atmospheric conditions. Spectra of air were measured in an oven at temperatures ranging from 300K to 1500 K. These spectra contained rovibrational lines from water and OH. The water spectra were compared to simulations from the HITRAN and HITEMP databases. Furthermore, spectra were recorded in the flame of a flat methane/air burner and in an oxyacetylene flame produced by a welding torch. The results show that cavity enhanced absorption spectroscopy provides a sensitive method for rapid monitoring of species in radiative environments.

Fluorination is a potent method to modulate chemical properties of glycans. Here, we study how C3- and C6-fluorination of glucosyl building blocks influence the structure of the intermediate of the glycosylation reaction, the glycosyl cation. Using a combination of gas-phase infrared spectroscopy and first-principles theory, glycosyl cations generated from fluorinated and non-fluorinated monosaccharides are structurally characterized. The results indicate that neighboring group participation of the C2-benzoyl protecting group is the dominant structural motif for all building blocks, correlating with the β-selectivity observed in glycosylation reactions. The infrared signatures indicate that participation of the benzoyl group in enhanced by resonance effects. Participation of remote acyl groups such as Fmoc or benzyl on the other hand is unfavored. The introduction of the less bulky fluorine leads to a change in the conformation of the ring pucker, whereas the structure of the active dioxolenium site remains unchanged.

Recently, a decelerator for neutral polar molecules has been presented that operates on the basis of macroscopic, three-dimensional, traveling electrostatic traps (Osterwalder et al., Phys. Rev. A 81, 051401 (2010)). In the present paper, a complete description of this decelerator is given, with emphasis on the electronics and the mechanical design. Experimental results showing the transverse velocity distributions of guided molecules are shown and compared to trajectory simulations. An assessment of non-adiabatic losses is made by comparing the deceleration signals from 13-CO with those from 12-CO and with simulated signals., 10 pages, 7 figures

both techniques. The b 1 S g (v852) X 3 Sg (v950) transition of molecular oxygen around 628 nm is used to demonstrate the possibility to selectively measure either the polarization-dependent absorption or the resonant magneto-optical rotation of gas-phase molecules in the appropriate setup. Just as in CRD absorption spectroscopy, where the rate of absorption is measured, in the here presented polarization-dependent CRD ~PDCRD! detection scheme the rate of polarization rotation is measured, which enables the polarization rotation to be quantitatively determined. Apart from studying electro-optic and magneto-optic phenomena on gas-phase species, the PDCRD detection scheme is demonstrated to be applicable to the study of magneto-optical rotation in transparent solid samples as well. © 1997 American Institute of Physics.@S0021-9606~97!00836-2# In 1988 O’Keefe and Deacon demonstrated a new direct absorption spectroscopic technique that can be performed with a pulsed light source and that has a significantly higher sensitivity than obtainable in ‘‘conventional’’ absorption spectroscopy. This so-called cavity ring down ~CRD! technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined in a closed optical cavity with a highQ factor. 1 The advantage over normal absorption spectroscopy results from ~i! the intrinsic insensitivity of the CRD technique to light source intensity fluctuations, and ~ii! the extremely long effective path lengths ~many kilometers! that can be realized in stable optical cavities. Since the technique is based on a pulsed measurement, it can be used in combination with pulsed molecular beams 2‐4 and it can also be used to study dynamical processes via time-resolved absorption measurements. 5 As long as mirrors with a sufficiently high reflectivity, detectors with a sufficiently fast time response, and tunable ~pulsed! light sources are available there is no intrinsic limitation to the spectral region in which CRD can be applied. By now, successful application of CRD spectroscopy has been demonstrated from the uv part of the spectrum 6 to the ir spectral region. 7,8 The application of CRD is most straightforward if it can be assumed that the linewidth of the light source can be neglected relative to the width of the molecular absorption. It has been shown, however, that if this assumption is no longer valid, one can still extract the correct absorption coefficient from the measured transients, provided the spectral intensity distribution of the light source is known. 6,9 As a consequence, it has been experimentally demonstrated that one does not necessarily need a narrow-band pulsed laser to perform a CRD experiment. One might just as well use a polychromatic light source and extract the spectral information after spectrally dispersing the light exiting the cavity, either in a monochromator or by using a Fourier transform spectrometer. 8,10

Mass selective gas-phase infrared spectroscopy using pulsed, high power InfraRed (IR) radiation produced by the Free Electron Laser (FEL) `Free Electron Laser for Infrared eXperiments' (FELIX) is demonstrated. Two complementary excitation schemes are used. In the first experiment, para amino benzoic acid (PABA) is infrared excited using FELIX and then ionized using a vacuum ultraviolet (VUV) F2 laser. In the second experiment, C60 is multiphoton excited by FELIX to energies high enough that the molecule can undergo autoionization. In both experiments, spectra are obtained by monitoring the ion of interest as a function of IR wavelength in the 100–2000 cm−1 range. It is demonstrated that these spectra contain the same information as direct IR absorption spectra. The sensitivity of these methods, however, is many orders of magnitude higher than that of conventional IR absorption spectroscopy. Details of the two different ionization mechanisms are discussed.

In a cavity ring down experiment the multi-mode structure of a short resonant cavity has been explicitly manipulated to allow a high spectral resolution, which is advantageous for the overall detection sensitivity as well. Coherent cavity ring down spectroscopy is performed around 298 nm on OH in a flame.

Gas-phase fullerenes are resonantly heated by a train of high power subpicosecond pulses from a free electron laser (FEL) to internal energies at which they efficiently undergo delayed ionization. When the laser is tuned from 6-20 mu m while the amount of laser produced parent ions is recorded, resonant absorption of 200-600 IR photons, resulting in almost fragmentation-free ion spectra, is observed. Infrared resonance enhanced multiphoton ionization with a FEL is shown to enable extremely sensitive IR spectroscopy with mass selective detection of gas-phase fullerenes. [S0031-9007(97)04923-5].

A compact open-path optical ammonia detector is developed. A tunable external-cavity diode laser operating at 1.5 μm is used to probe absorptions of ammonia via the cavity-enhanced absorption (CEA) technique. The detector is tested in a climate chamber. The sensitivity and linearity of this system are studied for ammonia and water at atmospheric pressure. A cluster of closely spaced rovibrational overtone and combination band transitions, observed as one broad absorption feature, is used for the detection of ammonia. On these molecular transitions a detection limit of 100 ppb (1 s) is determined. The ammonia measurements are calibrated independently with a chemiluminescence monitor. Compared to other optical open-path detection methods in the 1–2 μm region, the present result shows an improved sensitivity for contactless ammonia detection by over one order of magnitude. Using the same set-up, a detection limit of 100 ppm (1 s) is determined for the detection of water at atmospheric pressure.

We have accumulated large pure carbon clusters (Fullerenes) on a surface. These clusters were produced by laser vaporization of graphite in a static rare‐gas atmosphere. Their presence on the surface was confirmed by an isotope scrambling experiment using a laser‐desorption/laser‐ionization mass spectrometric detection scheme.

CO molecules in a supersonic molecular beam are resonantly excited from the X 1SIGMA+, upsilon" = 0 ground state to the a 3PI, upsilon' = 0 metastable state using pulsed laser radiation at 206 nm. In the excitation region a static electric field is applied to split individual M components of a given rotational line of this electronic transition. The splitting can be made larger than the Fourier-limited bandwidth of the pulsed radiation source and specific M levels in the a 3PI state can be populated. Peak fluxes of 10(17) (10(15)) oriented CO a 3PI1, upsilon' = 0, J' = 1, M' = 1 (a 3PI2, upsilon' = 0, J' = 2, M' = 2) molecules per second are obtained.

A novel instrumental setup for measuring infrared photodissociation spectra of buffer gas cooled, mass‐selected ions is described and tested. It combines a cryogenically cooled, linear radio frequency ion trap with a tandem mass spectrometer, optimally coupling continuous ion sources to pulsed laser experiments. The use of six independently adjustable DC potentials superimposed over the trapping radio frequency field provides control over the ion distribution within, as well as the kinetic energy distribution of the ions extracted from the ion trap. The scheme allows focusing the ions in space and time, such that they can be optimally irradiated by a pulsed, widely tunable infrared photodissociation laser. Ion intensities are monitored with a time‐of‐flight mass spectrometer mounted orthogonally to the ion trap axis.

Single crystal of pure C70 are grown from the vapour phase and the structure and morphology of these crystals is studied. By means of X-ray diffraction and TEM measurements five different phases are observed. The observed phases are (from high to low temperatures) fcc, rhombohedral, ideal hcp (c/a=1.63), deformed hcp (c/a=1.82) and a monoclinic phase. The occurrence of these different phases and the phase transitions is accounted for in a simple model. For the monoclinic structure a model for the stacking of the orientationally ordered molecules in the lattice is proposed. For both the hcp and fcc phases a Lennard-Jones type interaction potential is used to calculate bond strengths, lattice energies and the theoretical morphology.

Meteorites contain micrometer-sized graphite grains with embedded titanium carbide grains. Although isotopic analysis identifies asymptotic giant branch stars as the birth sites of these grains, there is no direct observational identification of these grains in astronomical sources. We report that infrared wavelength spectra of gas-phase titanium carbide nanocrystals derived in the laboratory show a prominent feature at a wavelength of 20.1 micrometers, which compares well to a similar feature in observed spectra of postasymptotic giant branch stars. It is concluded that titanium carbide forms during a short (approximately 100 years) phase of catastrophic mass Loss (>0.001 solar masses per year) in dying, Low-mass stars.

Gas-phase C84 is resonantly excited using infrared (IR) radiation from a free electron laser. At specific wavelengths, strong ion signals are observed, resulting from thermionic emission of electrons by the fullerenes. The mass-selected ion yield is recorded as a function of IR frequency and the resulting spectrum yields information on the electronic ground state of the gas-phase molecule.

Gas-phase C-60 molecules are excited with a 30 ps 266 nm Nd:YAG laser, followed by a train of high-power infrared (IR) sub-picosecond pulses from a free electron laser (FEL), which resonantly heats the molecules up to internal energies at which they efficiently undergo delayed ionization. By tuning the IR laser wavelength, IR-REMPI spectra are obtained. These are compared to simulations, giving detailed insight into the influence of UV pre-excitation on the IR laser ionization process of C-60 molecules. (C) 2000 Elsevier Science B.V. All rights reserved.

The ability to cool and manipulate atoms with light has yielded atom interferometry, precision spectroscopy, Bose-Einstein condensates and atom lasers. The extension of controlled manipulation to molecules is expected to be similarly rewarding, but molecules are not as amenable to manipulation by light owing to a far more complex energy-level spectrum. However, time-varying electric and magnetic fields have been successfully used to control the position and velocity of ions, suggesting that these schemes can also be used to manipulate neutral particles having an electric or magnetic dipole moment(1-4). Although the forces exerted on neutral species are many orders of magnitude smaller than those exerted on ions, beams of neutral dipolar molecules have been successfully slowed down in a series of pulsed electric fields(5,6) and subsequently loaded into an electrostatic trap(7). Here we extend the scheme to include a prototype electrostatic storage ring made of a hexapole torus with a circumference of 80 cm. After injection, decelerated bunches of deuterated ammonia molecules, each containing about 10(6) molecules in a single quantum state and with a translational temperature of 10 mK, travel up to six times around the ring. Stochastic cooling(8) might provide a means to increase the phase-space density of the stored molecules in the storage ring, and we expect this to open up new opportunities for molecular spectroscopy and studies of cold molecular collisions(9,10).

Mass selective gas-phase infrared spectroscopy using IR/VUV double resonance ionization is demonstrated. A free electron laser (FEL), tunable over the 100–2000 cm−1 range, is used as the IR excitation source while VUV light, produced by a F2 laser, is used for subsequent ionization. Spectra are obtained by monitoring the ion of interest as a function of IR wavelength. It is shown that these spectra can give the same information as direct IR absorption spectra. The sensitivity of the method is many orders of magnitude higher than that of conventional IR absorption spectroscopy. First results on para amino benzoic acid (PABA) are presented.

Kratschmer, Fostiropoulos and Huffman recently suggested that substantial quantities of C 60 are present in carbon deposits made by evaporating graphite under 100 Torr He quenching gas. We have directly confirmed the presence of fullerenes in such deposits using a surface-analytical mass-spectroscopic detection technique.

A new method for instantaneous temperature field measurements based on LIF studies of OH, O(2), and H(2)O in an open atmospheric flame with a tunable excimer laser is suggested. In this method the crucial problem of quenching at higher pressures is almost completely eliminated by excitation to a fast predissociating state. The various possible excitation and fluorescence processes that can be induced in the narrow tuning range of the KrF laser are characterized experimentally by excitation and dispersion spectra for the three molecules OH, O(2), and H(2)O. Of particular importance is the large power of the KrF laser, which allows efficient excitation of even weak transitions. The fast predissociation of these molecules in connection with the powerful excitation laser suggests that instantaneous temperature field measurements should be possible at higher pressures.