Core-penetrating Rydberg series of BaF: s~p~d~f supercomplexes

Towards a rational design of laser-coolable molecules: insights from equation-of-motion coupled-cluster calculations

Access to cold molecules is critical for quantum information science, design of new sensors, ultracold chemistry, and search of new phenomena.

Chirped-pulse millimeter-wave spectroscopy: spectrum, dynamics, and manipulation of Rydberg-Rydberg transitions

We apply the chirped-pulse millimeter-wave (CPmmW) technique to transitions between Rydberg states in calcium atoms. The unique feature of Rydberg-Rydberg transitions is that they have enormous electric dipole transition moments (~5 kiloDebye at n* ~ 40, where n* is the effective principal quantum number), so they interact strongly with the mm-wave radiation. After polarization by a mm-wave pulse in the 70-84 GHz frequency region, the excited transitions re-radiate free induction decay (FID) at their resonant frequencies, and the FID is heterodyne-detected by the CPmmW spectrometer. Data collection and averaging are performed in the time domain. The spectral resolution is ~100 kHz. Because of the large transition dipole moments, the available mm-wave power is sufficient to polarize the entire bandwidth of the spectrometer (12 GHz) in each pulse, and high-resolution survey spectra may be collected. Both absorptive and emissive transitions are observed, and they are distinguished by the phase of their FID relative to that of the excitation pulse. With the combination of the large transition dipole moments and direct monitoring of transitions, we observe dynamics, such as transient nutations from the interference of the excitation pulse with the polarization that it induces in the sample. Since the waveform produced by the mm-wave source may be precisely controlled, we can populate states with high angular momentum by a sequence of pulses while recording the results of these manipulations in the time domain. We also probe the superradiant decay of the Rydberg sample using photon echoes. The application of the CPmmW technique to transitions between Rydberg states of molecules is discussed.

Rubidium on Helium Droplets: Analysis of an Exotic Rydberg Complex for n* < 20 and 0 ≤ l ≤ 3

Rubidium atom Rydberg states perturbed by helium droplets of different sizes provide insight into the role of a nanosized dielectric on the Coulomb potential. The observation of droplet size-dependent shifts of excited states with respect to bare atom states is explained by a decreased quantum defect and a lowered ionization threshold. Within the scope of a Rydberg model, we demonstrate that quantum defects and ionization potentials are constant for each specific Rydberg series, which confirms the Rydberg character of excited Rubidium states on helium droplets. A set of six Rydberg series could be identified. Individual Rydberg states are observed with effective principal quantum numbers up to n* ≈ 19 and l ≤ 3, for which the expectation value of the electron orbital radius is about 10 times larger than the droplet radius.

Core-Penetrating Rydberg Series of BaF: Single-State and Two-State Fits of New Electronic States in the 4.4 </= n* </= 14.3 Region

We report results of optical-optical double-resonance studies of the Rydberg states of the BaF molecule in the energy region of E = 33 100-38 200 cm(-1) (4.4 </= n* </= 14.3). Barium monofluoride molecules have been produced in a resistively heated high-temperature oven from BaF(2) powder mixed with a small amount of boron powder. We have observed more than 50 new electronic states. Forty-nine of them have been rotationally analyzed and assigned to eight Rydberg series (four (2)Sigma(+), one (2)Pi, two (2)Delta, and one (2)Phi). Single-state and two-state fits have been carried out. Multiple local perturbations have been analyzed. Formation of supercomplexes in the Rydberg spectrum of BaF has been discussed. Copyright 2001 Academic Press.

The Electronic Structure of CaCl: Calculation by R Matrix and Generalized Quantum Defect Theory

The electronic spectrum of CaCl has been calculated using the variational eigenchannel R-matrix method combined with generalized multichannel quantum defect theory. The motion of the unpaired (Rydberg) electron is represented as a double scattering process on the closed-shell Ca(++) and Cl(-) core ions. Electron penetration into Ca(++) is taken into account as well as polarization effects. The partial saturation of the Cl(-) free-ion polarizability is evaluated on the basis of an ab initio calculation of the dipole and quadrupole moments of the CaCl(+) ion core. The calculations reproduce the effective principal quantum numbers nu of the experimentally known states (including the ground state) to within approximately 0.04. States with high-orbital angular momentum up to l = 6 are predicted. Copyright 1999 Academic Press.

Thermochemical Properties (D degrees0 and IP) of the Lanthanide Monohalides

Thermochemical data for the lanthanide monohalides have been combined with recent ligand field theory calculations (A. L. Kaledin, M. C. Heaven, R. W. Field, and L. A. Kaledin (1996). J. Mol. Spectrosc. 179, 310) to estimate the dissociation energies and ionization potentials for all LnX (where Ln in Ba through Lu, and X in F, Cl, Br, or I) molecules and the dissociation energies for the LnX+ ions. Owing to the negligible involvement of the core-like 4f electrons in bonding, the dissociation energies and ionization potentials of all LnX molecules, where Ln in Ba through Lu, and X in O, S, F, Cl, Br, or I, should vary with Ln atom in a simple linear manner, provided that corrections are made for differences in f-orbital occupancy between the LnX molecule and the free Ln atom or between the LnX molecule and the LnX+ molecular ion. We provide such a model here and, in so doing, correct several inconsistencies in the thermochemical data. Based on thermochemical data (A. A. Kitaev, I. S. Gotkis, P. G. Val'kov, and K. C. Krasnov (1996). Russ. Chem. Phys. 7, 1685) and recent spectroscopic observations (M. C. McCarthy, J. C. Bloch, R. W. Field, and L. A. Kaledin (1996) J. Mol. Spectrosc. 179, 251), a revised value for the ionization potential of DyF, IP(DyF) = 5.85 +/- 0.06 eV, is proposed. Copyright 1999 Academic Press.

Double-Resonance Spectroscopic Studies of Core-Penetrating Rydberg States of CaCl

Six core-penetrating Rydberg series have been assigned in the CaCl molecule by a combination of double-resonance spectroscopic techniques. Two 2Sigma+ series, with approximate quantum defects (delta) of 0.51 and 0.25, have been observed with effective principal quantum numbers (n*) in the range of 5-8 using the D2Sigma+ state as the resonant intermediate state for REMPI and/or ion-dip detection. A third 2Sigma+ series with delta approximately 0.84 and a 2Delta series with delta approximately 0.95 have been observed with n* = 16-18 using the A2Pi3/2 state as the resonant intermediate state for preparation of v+ = 1 vibrationally autoionizing states. Two additional series in the same region with delta approximately 0.90 and 0.07 are tentatively identified as the expected core-penetrating 2Pi series. Vibrational assignments have been confirmed in many cases on the basis of isotope shifts between the 35Cl and 37Cl isotopomers. The ion-dip and REMPI spectra display linewidths systematically broadened by predissociation. In addition to the assigned core-penetrating series, both the REMPI and the ion-dip spectra display some sharper features that have not yet been assigned. These sharper features most likely arise from perturbations of optically "bright" core-penetrating states by nominally "dark" higher-l core-nonpenetrating states. Copyright 1999 Academic Press.