Electronic bands of ScC in the region 620 - 720 nm

ScC molecules have been observed by laser-induced fluorescence, following the reaction of laser-ablated scandium metal with acetylene under supersonic jet-cooled conditions. Rotational analyses have been carried out for about 40 bands of Sc${}^{12}$C and Sc${}^{13}$C in the region 14000 - 16000 cm$^{-1}$. Two lower states are found, with $\Omega$ = 3/2 and 5/2, indicating that the ground state is $^4\Pi_i$ or $^2\Delta$. As yet we cannot distinguish between these alternatives, but note that the ground state of the isoelectronic YC molecule\footnote{B. Simard, P.A. Hackett and W.J. Balfour, Chem. Phys. Lett., {\bf 230}, 103 (1994).} is $^4\Pi_i$. The ground state bond length in ScC is 1.95${}_5$ \AA, and the vibrational frequency is 712 cm$^{-1}$. At least eight electronic transitions occur in the region studied, the majority obeying the selection rule $\Delta$$\Omega$ = +1. Rotational perturbations are widespread, consistent with a high density of excited electronic states

On the potentiality of abstract sounds in perception research

International audienceRecognition of sound sources and events is an important process 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 recognition 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

THE LOW-LYING ELECTRONIC STATES OF SCANDIUM MONOCARBIDE, ScC

Extensive wavelength-resolved fluorescence studies have been carried out for the electronic bands of ScC and Sc${}^{13}$C lying in the range 14000 - 16000 cm$^{-1}$. Taken together with detailed rotational analyses of these bands, these studies have clarified the natures of the low-lying electronic states. The ground state is an $Omega$ = 3/2 state, with a vibrational frequency of 648 cm$^{-1}$, and the first excited electronic state is an $Omega$ = 5/2 state, with a frequency of 712 cm$^{-1}$, lying 155.54 cm$^{-1}$ higher. These states are assigned as the lowest spin-orbit components of X$^2Pi_i$ and a$^4Pi_i$, respectively. The quartet nature of the a state is confirmed by the observation of the $^4Pi_{3/2}$ component, 18.71 cm$^{-1}$ above the $^4Pi_{5/2}$ component. The strongest bands in the region studied are two $^4Delta_{7/2}$ - $^4Pi_{5/2}$ transitions, where the upper states lie 14355 and 15445 cm$^{-1}$ above X$^2Pi_{3/2}$. Extensive doublet-quartet mixing occurs, which results in some complicated emission patterns. The energy order, a$^4Pi$ above X$^2Pi$, is consistent with the ab initio calculations of Kalemos et al.,footnote{ A. Kalemos, A. Mavridis and J.F. Harrison, J. Phys. Chem. {bf A155}, 755 (2001).} but differs from that found by Simard et al in the isoelectronic YC molecule.footnote{B. Simard, P.A. Hackett and W.J. Balfour, Chem. Phys. Lett., {bf 230}, 103 (1994).

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

Probing cis-trans isomerization in the S1 state of C2H2 via H-atom action and hot band-pumped IR-UV double resonance spectroscopies

We report novel experimental strategies that should prove instrumental in extending the vibrational and rotational assignments of the S1 state of acetylene, C[subscript 2]H[subscript 2], in the region of the cis-trans isomerization barrier. At present, the assignments are essentially complete up to ∼500 cm[superscript −1] below the barrier. Two difficulties arise when the assignments are continued to higher energies. One is that predissociation into C[subscript 2]H + H sets in roughly 1100 cm[superscript −1] below the barrier; the resulting quenching of laser-induced fluorescence (LIF) reduces its value for recording spectra in this region. The other difficulty is that tunneling through the barrier causes a staggering in the K-rotational structure of isomerizing vibrational levels. The assignment of these levels requires data for K values up to at least 3. Given the rotational selection rule K' − ℓ" = ± 1, such data must be obtained via excited vibrational levels of the ground state with ℓ" > 0. In this paper, high resolution H-atom resonance-enhanced multiphoton ionization spectra are demonstrated to contain predissociated bands which are almost invisible in LIF spectra, while preliminary data using a hyperthermal pulsed nozzle show that ℓ" = 2 states can be selectively populated in a jet, giving access to K' = 3 states in IR-UV double resonance.United States. Department of Energy (Grant No. DE-FG0287ER13671)Chinese Academy of Sciences (Distinguished Visiting Professorship)Natural Sciences and Engineering Research Council of Canada (NSERC

Spectroscopic characterization of isomerization transition states

Transition state theory is central to our understanding of chemical reaction dynamics. We demonstrate a method for extracting transition state energies and properties from a characteristic pattern found in frequency-domain spectra of isomerizing systems. This pattern—a dip in the spacings of certain barrier-proximal vibrational levels—can be understood using the concept of effective frequency, ω[superscript]eff. The method is applied to the cis-trans conformational change in the S[subscript 1] state of C[subscript 2]H[Subscript 2] and the bond-breaking HCN-HNC isomerization. In both cases, the barrier heights derived from spectroscopic data agree extremely well with previous ab initio calculations. We also show that it is possible to distinguish between vibrational modes that are actively involved in the isomerization process and those that are passive bystanders.National Science Foundation (U.S.) (NSF Graduate Research Fellowship DGE 1144083)Alexander von Humboldt-Stiftung (Feodor Lynen fellowship)United States. Department of Energy (Grant DE-FG0287ER136

Cystic hygroma and potential airway obstruction in a newborn: a case report and review of the literature

BACKGROUND: Cervical cystic hygroma is a benign congenital malformation of the lymphatic system. Incidence of cystic hygroma is 1/6000 live births. We present a case of right neck mass with potential respiratory compromise in a newborn. CASE PRESENTATION: The patient was a full term baby girl with an incidental finding of right neck mass which was described on ultrasound and magnetic resonance imaging as a cystic lesion in the nasopharynx and right neck which inferiorly followed the course of the right carotid artery, consistent with cystic hygroma. She started with respiratory compromise, and a follow-up magnetic resonance imaging showed increased size of the cystic hygroma. Dexamethasone was started to reduce fluid build up in the mass. When the cystic hygroma was found to be inseparable from the right half of the thyroid gland, the otolaryngologist performed hemithyroidectomy. CONCLUSION: The patient had neuropraxia involving the marginal mandibular branch of the facial nerve, which was expected to correct with time. Large cervical cystic hygromas may surround or displace neurovascular structures making their identification quite challenging intraoperatively. A team of experienced surgeons will help to ensure a successful surgical outcome

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