Two distinct high-accuracy laboratory spectroscopic investigations of the H 2 molecule are reported. Anchor lines in the EF 1 AE þ g À X 1 AE þ g system are calibrated by two-photon deep-UV Doppler-free spectroscopy, while independent Fourier-transform spectroscopic measurements are performed that yield accurate spacings in the B 1 AE þ u À EF 1 AE þ g and I 1 Å g À C 1 Å u systems. From combination differences accurate transition wavelengths for the B À X Lyman and the C À X Werner lines can be determined with accuracies better than $5 Â 10 À9 , representing a major improvement over existing values. This metrology provides a practically exact database to extract a possible variation of the proton-to-electron mass ratio based on H 2 lines in high-redshift objects. Moreover, it forms a rationale for equipping a future class of telescopes, carrying 30-40 m dishes, with novel spectrometers of higher resolving powers. DOI: 10.1103/PhysRevLett.101.223001 PACS numbers: 33.20.Àt, 06.20.Jr, 95.30.Dr, 98.80.Bp Fundamental physical constants may be subject to change on cosmological time scales. For the fine structure constant , evidence for a temporal drift with a 5 significance has been reported [1]. Recently, an indication of a possible decrease of the dimensionless proton-to-electron mass ratio ¼ m p =m e was reported at Á= ¼ ð2:45 AE 0:59Þ Â 10 À5 over a time interval of 12 Â 10 9 years, based on a comparison of spectra of molecular hydrogen [2,3]. The latter findings require three crucial input ingredients. First, a theory is required that relates possible changes in to observable shifts in the spectrum of H 2 . For this purpose sensitivity coefficients K i ¼ d ln i =d ln, which indicate how each line in the H 2 spectrum would drift as a result of a variation in the mass ratio , can be deduced either in a semiempirical fashion [3] or through quantum chemical ab initio calculations [4]. The second ingredient is the accurate determination of spectral line positions at high redshifts. Of the thousands of known quasar systems at redshifts z > 2, H 2 absorption features have only been observed in some 10 to 15 systems thus far. Of these, only Q0405-443 and Q0347-383 have high-quality and well-calibrated spectra containing many H 2 lines [5], which formed the basis of the finding on Á= [2]. Recently, HE0027-184 was established as another system with many resolved H 2 lines [6], and hence a potential source in deriving further constraints on Á. The final ingredient is a database comprising of high-precision laboratory measurements that represent present-day (z ¼ 0) H 2 spectra. The limited amount of available astrophysical data accentuates the need for a set of laboratory data that would not contribute to the uncertainties in estimating a possible drift in .The principle behind the novel determination of laboratory transition wavelengths in theWerner band systems is depicted in Fig. 1. Two entirely independent experiments are performed. First, the level energies of the lowest rotational states in. Schematic of the combi...

-Results are presented from experimental investigations of oscillatory phenomena in an electron beam with a virtual cathode in a diode gap with a decelerating field. Experiments have revealed a stochastic broadband generation of the microwave oscillations of a virtual cathode in a decelerating field. Numerical simulations based on a simple one-dimensional model have shown that the onset of the stochastic generation and the broadening of the oscillation spectrum with increasing beam deceleration rate are governed by the processes of regrouping of the electrons in a beam with a virtual cathode.

Results are presented from numerical modeling of the effect of the inhomogeneity of the ion background on the complicated spatiotemporal dynamics of an electron beam with a virtual cathode in plane geometry. The possibility is demonstrated of increasing the generation frequency without changing the beam current. The spatiotemporal structures that form in the beam and govern the complicated stochastic dynamics of the nonuniform electron-plasma system under consideration are investigated by the methods of wavelet bicoherence and by analyzing the calculated electron trajectories on the space-time diagrams.

The space-time dynamics of electron domains in a semiconductor superlattice is studied in a tilted magnetic field with regard to the effect of temperature. It is shown that an increase in temperature sub stantially changes the space-time dynamics of the system. This leads to a decrease in the frequency and amplitude of oscillations of a current flowing through the semiconductor superlattice. The quenching of oscillations is observed, which is attributed to the change in the drift velocity as a function of electric field strength under the variation of temperature.

We reinvestigated the 2 + 1 REMPI Q-branch spectrum of the a''1Sigma(g)+-X1Sigma(g)+ system of N2 at around 202 nm in a Doppler-free configuration with counterpropagating laser beams. Highly accurate absolute calibrations were performed using either an I2 reference standard or a frequency comb reference laser. The observed rotational series shows a clear effect of a perturbation in terms of an anticrossing located at J = 26. In addition to the improved set of molecular constants for the a''1Sigma(g)+ state, we tentatively assign the perturber state to be the 1Sigma(g)+(II) state of N2.