11 research outputs found
Observation of b symmetry vibrational levels of the SO \tilde{\mbox{C}} B state: Vibrational level staggering, Coriolis interactions, and rotation-vibration constants
The B state of SO has a double-minimum
potential in the antisymmetric stretch coordinate, such that the minimum energy
geometry has nonequivalent SO bond lengths. However, low-lying levels with odd
quanta of antisymmetric stretch (b vibrational symmetry) have not
previously been observed because transitions into these levels from the
zero-point level of the state are vibronically forbidden.
We use IR-UV double resonance to observe the b vibrational levels of the
state below 1600 cm of vibrational excitation. This
enables a direct characterization of the vibrational level staggering that
results from the double-minimum potential. In addition, it allows us to
deperturb the strong -axis Coriolis interactions between levels of a and
b vibrational symmetry, and to determine accurately the vibrational
dependence of the rotational constants in the distorted
electronic state
OBSERVATION OF LEVEL-SPECIFIC PREDISSOCIATION RATES IN S1 ACETYLENE
A new spectroscopic scheme was used to gain insight into the predissociation mechanisms of the S electronic state of acetylene in the 47000-47300 cm region. To study this mechanism, H-atom action spectra of predissociative S were recorded. Instead of detecting H-atom via REMPI, an H-atom fluorescence scheme was developed, in which the H-atom was excited to 3s and 3d levels and the fluorescence was detected. The signal-to-noise ratio of H-atom fluorescence-detected action spectra is superior to REMPI detected H-atom spectra. By comparing the LIF and H-atom spectra, there is direct evidence of level-dependent predissociation rates. Some of the line-widths observed in the H-atom spectra are broader than in the LIF spectra, confirming the triplet-mediated nature of S acetylene
Angular momentum in rotating superfluid droplets
The angular momentum of rotating superfluid droplets originates from quantized vortices and capillary waves, the interplay between which remains to be uncovered. Here, the rotation of isolated submicrometer superfluid 4He droplets is studied by ultrafast x-ray diffraction using a free electron laser. The diffraction patterns provide simultaneous access to the morphology of the droplets and the vortex arrays they host. In capsule-shaped droplets, vortices form a distorted triangular lattice, whereas they arrange along elliptical contours in ellipsoidal droplets. The combined action of vortices and capillary waves results in droplet shapes close to those of classical droplets rotating with the same angular velocity. The findings are corroborated by density functional theory calculations describing the velocity fields and shape deformations of a rotating superfluid cylinder
Recommended from our members
Angular Momentum in Rotating Superfluid Droplets.
The angular momentum of rotating superfluid droplets originates from quantized vortices and capillary waves, the interplay between which remains to be uncovered. Here, the rotation of isolated submicrometer superfluid ^{4}He droplets is studied by ultrafast x-ray diffraction using a free electron laser. The diffraction patterns provide simultaneous access to the morphology of the droplets and the vortex arrays they host. In capsule-shaped droplets, vortices form a distorted triangular lattice, whereas they arrange along elliptical contours in ellipsoidal droplets. The combined action of vortices and capillary waves results in droplet shapes close to those of classical droplets rotating with the same angular velocity. The findings are corroborated by density functional theory calculations describing the velocity fields and shape deformations of a rotating superfluid cylinder
Angular Momentum in Rotating Superfluid Droplets
The angular momentum of rotating superfluid droplets originates from quantized vortices and capillary waves, the interplay between which remains to be uncovered. Here, the rotation of isolated submicrometer superfluid He-4 droplets is studied by ultrafast x-ray diffraction using a free electron laser. The diffraction patterns provide simultaneous access to the morphology of the droplets and the vortex arrays they host. In capsule-shaped droplets, vortices form a distorted triangular lattice, whereas they arrange along elliptical contours in ellipsoidal droplets. The combined action of vortices and capillary waves results in droplet shapes close to those of classical droplets rotating with the same angular velocity. The findings are corroborated by density functional theory calculations describing the velocity fields and shape deformations of a rotating superfluid cylinder
Aggregation of solutes in bosonic versus fermionic quantum fluids.
Quantum fluid droplets made of helium-3 (3He) or helium-4 (4He) isotopes have long been considered as ideal cryogenic nanolabs, enabling unique ultracold chemistry and spectroscopy applications. The droplets were believed to provide a homogeneous environment in which dopant atoms and molecules could move and react almost as in free space but at temperatures close to absolute zero. Here, we report ultrafast x-ray diffraction experiments on xenon-doped 3He and 4He nanodroplets, demonstrating that the unavoidable rotational excitation of isolated droplets leads to highly anisotropic and inhomogeneous interactions between the host matrix and enclosed dopants. Superfluid 4He droplets are laced with quantum vortices that trap the embedded particles, leading to the formation of filament-shaped clusters. In comparison, dopants in 3He droplets gather in diffuse, ring-shaped structures along the equator. The shapes of droplets carrying filaments or rings are direct evidence that rotational excitation is the root cause for the inhomogeneous dopant distributions
Charging and ion ejection dynamics of large helium nanodroplets exposed to intense femtosecond soft X-ray pulses
Ion ejection from charged helium nanodroplets exposed to intense femtosecond soft X-ray pulses is studied by single-pulse ion time-of-flight (TOF) spectroscopy in coincidence with small-angle X-ray scattering. Scattering images encode the droplet size and absolute photon flux incident on each droplet, while ion TOF spectra are used to determine the maximum ion kinetic energy, , of fragments (j = 1–4). Measurements span droplet sizes between and (radii = 78–578 nm), and droplet charges between and e/atom. Conditions encompass a wide range of ionization and expansion regimes, from departure of all photoelectrons from the droplet, leading to pure Coulomb explosion, to substantial electron trapping by the electrostatic potential of the charged droplet, indicating the onset of hydrodynamic expansion. The unique combination of absolute X-ray intensities, droplet sizes, and ion on an event-by-event basis reveals a detailed picture of the correlations between the ionization conditions and the ejection dynamics of the ionic fragments. The maximum of He is found to be governed by Coulomb repulsion from unscreened cations across all expansion regimes. The impact of ion-atom interactions resulting from the relatively low charge densities is increasingly relevant with less electron trapping. The findings are consistent with the emergence of a charged spherical shell around a quasineutral plasma core as the degree of ionization increases. The results demonstrate a complex relationship between measured ion and droplet ionization conditions that can only be disentangled through the use of coincident single-pulse TOF and scattering data