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Examines the millimeter and submillimeter-wave molecular beam spectrum of the perdeuterated ammonia dimer between 50 and 400 GHz using electric-resonance optothermal spectrometer. Internal rotation complicating the spectrum; Tunneling motions that split the rigid molecule energy levels; Transitions for rotation-tunneling states.

Part II. Reports on the fully coupled six-dimensional calculations of the water dimmer vibration-rotation-tunneling (VRT) states with split Wigner pseudospectral (SWPS) approach. Feasible tunneling motions of the water dimmer and how they are manifested in the microwave and VRT spectra; Overview on the SWPS method and improvements applied to water dimmer.

Studies the O-H stretching vibrations of jet-cooled methanol clusters in direct absorption using infrared cavity ringdown laser absorption spectroscopy. Measurement of rovibrational bands; Measurement of both bonded and free O-H stretches for the dimer; Existence of methanol clusters larger than the dimer in cyclic ring configurations.

Dynamic etching methods for fabricating fibre optic tips are explored and modelled. By vertically translating the fibre during etching by an HF solution under an organic protective layer, a variety of tip shapes were created. The probe taper lengths, cone angles and geometrical probe shapes were measured in order to evaluate the dynamic meniscus etching process. Fibre motion, etching rate, meniscus distortion and etching time were all found to be important variables that can be used to control the final probe shape. [ABSTRACT FROM AUTHOR]

Soft x-ray absorption spectroscopy is a powerful probe of surface electronic and geometric structure in metals, semiconductors, and thin films. Because these techniques generally require ultrahigh vacuum, corresponding studies of volatile liquid surfaces have hitherto been precluded. We describe the design and implementation of an x-ray experiment based on the use of liquid microjets, permitting the study of volatile liquid surfaces under quasi-equilibrium conditions by synchrotron-based spectroscopy. The liquid microjet temperatures are also characterized by Raman spectroscopy, which connects our structural studies with those conducted on liquid samples under equilibrium conditions. In recent experiments, we have observed and quantified the intermolecular surface relaxation of liquid water and methanol and have identified a large population of “acceptor-only” molecules at the liquid water interface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Describes the basic principles, design considerations and applications of cavity ringdown laser absorption spectroscopy (CRLAS). Relationship between mirror reflectivity, absorption sensitivity and cavity ringdown time; Design constraints on the ringdown cavity geometry; Applications in flame and plasma diagnostics and chemical kinetics; Fourier transform-CRLAS.

Reports on research in which the linear and nonlinear optical responses of Langmuir monolayers of organically functionalized silver quantum dots were measured as a continuous function of interparticle separation under near-ambient conditions. Circumstances under which the transition was reversible; Methods used in the research.

Reports a detailed study of the water trimer. Questions of impact on many chemical and biological problems; Intermolecular forces that act among water molecules; The concerted hydrogen-bond tunneling motions that occur in condensed phases and in gaseous water clusters; Chiral six-membered ring structure with rapid quantum tunneling occurring between the enantiomers; Vibration involving torsional motion of water subunits about each hydrogen bond axis.

Terahertz laser VRT spectra of the water dimer consisting of 731 transitions measured with an average precision of 2 MHz and involving four (D[sub 2]O)[sub 2] intermolecular vibrations (one previously published) have been measured between 65 and 104 cm[sup -1]. The precisely determined energy level patterns differ both qualitatively and quantitatively from the predictions of several dimer potentials tested, and reveal an ordering of the intermolecular vibrations which differs dramatically from that predicted by standard normal mode analysis. Strong coupling is indicated between the low barrier tunneling motions and the intermolecular vibrations as well as among different vibrations. Particularly, the 83 cm[sup -1] (acceptor wag) and 90 cm[sup -1] (D[sub 2]O)[sub 2] (acceptor twist) vibrations interact through a Coriolis perturbation. These spectra provide the basis for our recent determination of the water pair potential. The corresponding data set for (H[sub 2]O)[sub 2] is presented in an accompanying paper. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Terahertz VRT laser spectra of four (H[sub 2]O)[sub 2] intermolecular vibrations consisting of 362 transitions have been measured between 87 and 108 cm[sup -1] with ca. 2 MHz precision. The results differ both qualitatively and quantitatively from the predictions of dimer potentials tested. The spectra also reveal an ordering of the intermolecular vibrations which differs dramatically from that predicted by normal mode analysis. Strong coupling is indicated between the low barrier tunneling motions and the intermolecular vibrations as well as among different vibrations. In particular the 102.1 cm[sup -1] (H[sub 2]O)[sub 2] vibration assigned as the acceptor wag (ν[sub 8]) exhibits two types of perturbations. In one of these a component of K[sub a]=1 coupling with a tunneling component of K[sub a]=0 in the 108 cm[sup -1] acceptor twist (ν[sub 11]) vibration. There is also an indication that the 103.1 cm[sup -1] (H[sub 2]O)[sub 2] band assigned as the donor in-plane bend (ν[sub 6]) is coupled to the acceptor wag resulting in a lower of the in-plane bend frequency and a higher acceptor wag frequency. Detailed analysis of the VRT levels confirms the extreme nonrigidity of this complex, indicating that the use of approximate models with reduced dimensionality to calculate its properties are likely to fail. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A simple technique for achieving high spectral resolution coherent anti-Stokes Raman scattering (CARS) spectra with a femtosecond laser system is presented. A linearly chirped and stretched (∼10 ps) pump pulse generates CARS signal only when overlapped in time with the Stokes pulse (90 fs), creating a `temporal slit'' that defines the spectral resolution of the technique. Multiplex CARS spectra for liquid methanol and liquid isooctane are presented, demonstrating a spectral resolution of better than 5 cm−1. This new chirped (c-CARS) technique should prove useful for chemically-selective imaging applications, as it significantly reduces the non-resonant background contribution. [Copyright &y& Elsevier]

The C3 molecule is of fundamental interest to chemists, both as the simplest cumulene and as a prototypical nonrigid system. It is also of great importance in astrophysics, as it now serves as a remote diagnostic of the temperature and density of interstellar clouds. However, high resolution astronomical spectra have uncovered a discrepancy between the observed R(0) transition and the laboratory spectrum. We have used cavity ringdown spectroscopy to obtain a high resolution, low temperature spectrum of the 4051 A˚ band, and have confirmed that the R(0) transition was incorrectly assigned in previous laboratory work. [Copyright &y& Elsevier]

Presents research that describes the determination of a polarizable water pair potential by regression analysis of the rotational constants, tunneling splittings, and intermolecular vibrational frequencies. Methods; Results; Conclusions.