M.O. Vieitez

Spectroscopic observation and characterization of H(+)H(-) heavy Rydberg states.

A series of discrete resonances was observed in the spectrum of H2, which can be unambiguously assigned to bound quantum states in the 1/R Coulombic potential of the H+H- ion-pair system. Two-step laser excitation was performed, using tunable extreme ultraviolet radiation at lambda = 94-96 nm in the first step, and tunable ultraviolet radiation in the range lambda = 310-350 nm in the second step. The resonances, detected via H+ and H2+ ions produced in the decay process, follow a sequence of principal quantum numbers (n = 140-230) associated with a Rydberg formula in which the Rydberg constant is mass scaled. The series converges upon the ionic H+H- dissociation threshold. This limit can be calculated without further assumptions from known ionization and dissociation energies in the hydrogen system and the electronegativity of the hydrogen atom. A possible excitation mechanism is discussed in terms of a complex resonance. Detailed measurements are performed to unravel and quantify the decay of the heavy Rydberg states into molecular H2+ ions, as well as into atomic fragments, both H(n = 2) and H(n = 3). Lifetimes are found to scale as n3.

A Rayleigh-Brillouin scattering spectrometer for ultraviolet wavelengths

A spectrometer for the measurement of spontaneous Rayleigh-Brillouin (RB) scattering line profiles at ultraviolet wavelengths from gas phase molecules has been developed, employing a high-power frequency-stabilized UV-laser with narrow bandwidth (2 MHz). The UV-light from a frequency-doubled titanium:sapphire laser is further amplified in an enhancement cavity, delivering a 5 W UV-beam propagating through the interaction region inside a scattering cell. The design of the RB-scattering cell allows for measurements at gas pressures in the range 0-4 bars and at stably controlled temperatures from -30 °C to 70 °C. A scannable Fabry-Perot analyzer with instrument resolution of 232 MHz probes the RB profiles. Measurements on N(2) and SF(6) gases demonstrate that the high signal-to-noise ratio is achievable with the instrument at the 1% level at the peak amplitude of the scattering profile.

Frequency calibration of B (1)Sigma(+)(u)-X (1)Sigma(+)(g) (6,0) Lyman transitions in H-2 for comparison with quasar data

The Lyman and Werner spectroscopic transitions of molecular hydrogen, the most ubiquitous molecular spectral lines observed in the universe, provide a tool to probe a possible variation of the proton-to-electron mass ratio mu on a cosmological time scale. Such procedures require a database of zero-redshift, or laboratory-based wavelengths at the highest possible level of accuracy. Accurate transitions in the B (1)Sigma(+)(u)-X (1)Sigma(+)(g) (6,0) Lyman band of H2 are still missing in the set of laboratory data, due to previously encountered problems in generating the appropriate wavelengths using a narrow-band extreme ultraviolet laser source. Here frequency calibrations of the missing transitions are presented from a laser-based study at a (5 - 8) x 10(-8) accuracy level.