Femtosecond Spectroscopy with Vacuum Ultraviolet Pulse Pairs

We combine different wavelengths from an intense high-order harmonics source with variable delay at the focus of a split-mirror interferometer to conduct pump-probe experiments on gas-phase molecules. We report measurements of the time resolution (<44 fs) and spatial profiles (4 {\mu}m x 12 {\mu}m) at the focus of the apparatus. We demonstrate the utility of this two-color, high-order-harmonic technique by time resolving molecular hydrogen elimination from C2H4 excited into its absorption band at 161 nm

Abstract sounds and their applications in audio and perception research

International audienceRecognition of sound sources and events is an important pro- cess in sound perception and has been studied in many research domains. Conversely sounds that cannot be recognized are not often studied except by electroacoustic music composers. Besides, considerations on recogni- tion of sources might help to address the problem of stimulus selection and categorization of sounds in the context of perception research. This paper introduces what we call abstract sounds with the existing musical background and shows their relevance for different applications

Electronic transitions of cobalt carbide, CoC, near 750 nm: a good example of case (b(betaS)) hyperfine coupling

The laser induced fluorescence spectrum of jet-cooled CoC near 750 nm has been measured at high resolution following the reaction of laser-ablated cobalt atoms with methane. The X2Σ+ ground state of CoC is an unusually good example of Hund's case (bβS) coupling. Since Co has a nuclear spin I=7/2, each rotational level is split by the Fermi contact interaction into G=3 and G=4 components, where G=I+S; the splitting for N=0 is more than 0.5 cm-1. The X2Σ+ state begins to uncouple toward case (bβJ) with increasing rotation. Transitions to various 2Π excited states occur in the region 13 000-14 500 cm-1; the most prominent of these (for which high resolution spectra have been recorded) lie at 13 079 cm-1 ( 2Π3/2) and 13 343 cm-1 (2Π 1/2). The (bβS) coupling in the ground state produces some unexpected hyperfine intensity patterns, which have been studied in detail. A very low-lying 2Δi state, whose Ω=5/2 and Ω=3/2 components lie at 221 and 1173 cm-1, has been identified. Laser excitation of the 2Π3/2- 2Δ5/2 transition has been observed by monitoring the strong 2Π3/2-X2Σ+ emission, which has allowed the 2Δ5/2 state to be characterized at high resolution. A total of 879 rotational-hyperfine transitions between the various 2Π1/2, 2Π3/2, 2Δ5/2, and 2Σ+ states have been assigned and fitted. Matrix elements for a 2Σ+ state in case (b βS) coupling are listed. © 1995 American Institute of Physics.M. Barnes, A. J. Merer and G. F. Meth

Reenacting sensorimotor features of drawing movements from friction sounds

International audienceEven though we generally don't pay attention to the friction sounds produced when we are writing or drawing, these sounds are recordable, and can even evoke the underlying gesture. In this paper, auditory perception of such sounds, and the internal representations they evoke when we listen to them, is considered from the sensorimotor learning point of view. The use of synthesis processes of friction sounds makes it possible to investigate the perceptual influence of each gestures parameter separately. Here, the influence of the velocity profile on the mental representation of the gesture induced by a friction sound was investigated through 3 experiments. The results reveal the perceptual relevance of this parameter, and particularly a specific morphology corresponding to biological movements, the so-called 1/3-power law. The experiments are discussed according to the sensorimotor theory and the invariant taxonomy of the ecological approach

Timbre from Sound Synthesis and High-level Control Perspectives

International audienceExploring the many surprising facets of timbre through sound manipulations has been a common practice among composers and instrument makers of all times. The digital era radically changed the approach to sounds thanks to the unlimited possibilities offered by computers that made it possible to investigate sounds without physical constraints. In this chapter we describe investigations on timbre based on the analysis by synthesis approach that consists in using digital synthesis algorithms to reproduce sounds and further modify the parameters of the algorithms to investigate their perceptual relevance. In the first part of the chapter timbre is investigated in a musical context. An examination of the sound quality of different wood species for xylophone making is first presented. Then the influence of instrumental control on timbre is described in the case of clarinet and cello performances. In the second part of the chapter, we mainly focus on the identification of sound morphologies, so called invariant sound structures responsible for the evocations induced by environmental sounds by relating basic signal descriptors and timbre descriptors to evocations in the case of car door noises, motor noises, solid objects, and their interactions

ORDER AND COMPLEXITY IN THE ELECTRONIC SPECTRA OF DIATOMIC TRANSITION METAL COMPOUNDS

Author Institution: Department of Chemistry, University of Britis ColumbiaDiatomic transition metal compounds, such as oxides and nitrides, have two types of low-lying excited electronic states; in one type electrons are permuted among the mental orbitals and, in the other type, the charge-transfer states, electrons are promoted from the light atom to the metal. The relative energies of these two types of states depend on the ionization potential of the metal. For the early transition metal compounds, where the I.P. of the metal is much lower than that of the light atom, the charge transfer states lie fairly high, so that the electronic spectra consist mainly of fairly simple well-separated transitions that are easily understood in the single configuration approximation. The later transition metal compounds have much lower-lying charge-transfer states. There are many more of these states than there are of the intra-metal states, and they interact strongly with each other and with the intra-metal states. The result is that the spectra degenerate into long overlapping and irregular vibrational progressions of extreme complexity. In any given region there are usually one or two ``bright"" states which carry the oscillator strength, and a host of perturbing ``dark"" states which pick up a small amount of intensity by a variety of mechanisms. Severe rotational perturbations occur in every observable vibrational level, and electronic assignments become virtually impossible. The most extreme examples of this effect studied so far occur in FeO and CoO. Nuclear hyperfine structure, for metals with odd atomic number such as V, Mn and Co, adds an additional dimension of complexity

ORBITAL ANGULAR MOMENTUM IN LINEAR MOLECULES CONTAINING TRANSITION METALS

Author Institution: Department of Chemistry, University of British ColumbiaVibronic coupling arises in the Born-Oppenheimer approximation from the cross-term that appears when the second derivative operator for the nuclear kinetic energy acts on the product of an electronic and a nuclear wave function. This cross-term is usually handled as an effective operator which has matrix elements between vibrational levels of different electronic states. In unsymmetrical linear triatomic molecules these elements follow the selection rules $\Delta \Lambda = \pm 1, \Delta l = \mp 1, \Delta v_{2} = \pm 1,$ where $\nu _{2}$ is the bending vibration. The most important effects occur in $\Pi$; electronic states, because distant $\Sigma^{+}$ and $\Sigma^{-}$ states affect the Born-Oppenheimer components differently. If the $\Sigma$ and $\Pi$ electronic states are well separated the vibrational structure of the $\Pi$ state can be treated as if there is an operator acting within the $\Pi$ state that causes a quadratic splitting between its two components; this is the essence of the Renner- Teller effect. In transition metal-containing molecules the density of electronic states can be high enough for this approach to break down. Every electronic transition then contains intense ``forbidden'' vibrational bands, violating the usual selection rules, and large numbers of seemingly random perturbations occur. Examples will be draw from the spectra of the metal methylidynes and hydroxides

POLYATOMIC RADICALS IN THE REACTION PRODUCTS OF LASER-ABLATED METALS WITH SIMPLE MOLECULES; SOME INTERESTING ELECTRONIC SPECTRA

Author Institution: INSTITUTE OF ATOMIC AND MOLECULAR SCIENCES, ACADEMIA SINICA, P.O. BOX 23-166, TAIPEI 10617, TAIWANSpectra of a number of transition metal-containing radicals have been observed following the reaction of laser-ablated metals with simple molecules. Among the species we have found are hydroxides (MOH), methylidynes (MCH), carbides (MC$_2$), imides (MNH) and cyanides (MCN). Except for YC$_2$, which is T-shaped, all the molecules we have studied are linear. Because of the density of electronic states in $d$ electron systems, vibronic coupling effects are very much more important than in light molecules. A good example is YOH, where the first order coupling between the close-lying \ {B}${}^1\Pi$ and \ {C}${}^1\Sigma$ states causes the molecule to become non-linear in the lower Born-Oppenheimer component of the \ {B}${}^1\Pi$ state. Strong vibronically-induced bands occur in almost all the observed electronic transitions, and in molecules containing heavy metals (e.g. LaNH) so much spin-orbit coupling may be transferred to the $l \neq$ 0 bending levels of $^2\Sigma$ electronic states that they follow case (a) coupling. Nevertheless, after all the complexities of orbital angular momentum, rotational perturbations and Fermi resonance have been taken into account, the underlying electronic structure is often very simple: the observed states of NiCN, for example, bear a surprisingly strong resemblance to those of NiH. Nuclear hyperfine effects are important when metals with odd atomic number are present: impressive magnetic dipole splittings occur in the \ {X}$^3\Delta$ states of VCH and NbCH, while the \ {X}$^1\Sigma^+$ state of TaCH shows some of the largest electric quadrupole splittings yet found in a molecule