John T. Bahns

First observation of bound–continuum transitions in the laser‐induced A 1Σ+u–X 1Σ+g fluorescence of Na2

We report an interesting spectrum of Na2 excited by a Kr+ (5682 A) laser which shows a long series of R–P doublets in the region 5600–8000 A and a continuum with three very broad maxima beyond 8000 A. Our spectral analysis reveals that the laser populates the v′=34, J′=50 level in the A1Σ+u state from where Na2 molecules fluoresce not only to the bound vibrational levels of the entire ground state potential well (3≤v″≤56) but also to the continuum levels above the well. We have made an independent theoretical quantitative prediction of the continuous emission and the agreement between experiment and theory is found to be excellent. Almost the entire (99.6%) ground state RKR potential is constructed using the bound state experimental data which leads to a more accurate value of the dissociation energy (D″e=6024±6 cm−1). The feasibility of a continuously tunable near infrared Na2 laser based upon this radiative dissociation process is discussed. Finally, we present a comprehensive bibliography for the Na2 m...

Laser cooling of molecules: A sequential scheme for rotation, translation, and vibration

A novel scheme is proposed for sequential cooling of rotation, translation, and vibration of molecules. More generally, this scheme manipulates and controls the states and energies of molecules. The scheme, while somewhat complex, is simpler and more feasible than simply providing a large number of synchronously but independently tunable lasers. The key component is a multiple single frequency laser (MSFL) in which a single narrow band pump laser generates an ensemble of resonant ‘‘stimulated Raman’’ (RSR) sidebands (subsequently amplified and selected) in a sample of the molecules to be cooled. Starting with a relatively cold molecular sample (e.g., a supersonic beam of Cs2), the rotation of molecules is cooled by sequential application of P branch electronic transition frequencies transverse to the molecular beam beginning at higher rotational angular momentum J. Then translation of molecules is cooled by application of multiple low J, P, and R branch transition frequencies which counterpropagate with t...

Formation of Cold (T ⩽ 1 K) Molecules

Publisher Summary This chapter illustrates that the formation of low-temperature molecules with translational energy distributions characterized by T ≤ K is reviewed. Such molecules can in principle be produced optically or nonoptically or by photoassociation of ultracold atoms. Recent results producing cold - and especially ultracold - alkali metal dmers and producing cold paramagnetic molecules are highlighted, along with their potential applications and scientific significance. It clarifies and summarizes the many proposals for formation of gas-phase molecules with subKelvin translational and internal temperatures (or average energies (divided by Boltzmanns constant k ) if not in a thermal distribution) and to discuss the exciting and very recent results achieved in implementing these proposals. However, for low-density, low-temperature atomic and molecular gases, the time required to reach true equilibrium (a solid) can be much longer than the corresponding experimental studies. Only the translational degrees of freedom clearly equilibrate thermally on a short time scale. The possibilities for nonthermal distributions among other (internal) degrees of freedom are great, as discussed in the chapter.

Electronic assignments of the violet bands of sodium

Abstract The puzzling violet bands of sodium ( ≈ 425-460 nm), known since 1932, are shown conclusively to arise from the superposition of two distinct continuum emission bands - one singlet (2 1 Σ + u → X 1 Σ + g ) and one triplet (primarily 2 3 Π g → 1 3 Π u + ). Each continuum emission system shows complex interference structure arising from multiple branches of the Mulliken difference potential.

Observation of gain in the violet bands of sodium vapor

We report our observations attributable to optical gain through stimulated emission in the violet when sodium vapor is optically pumped with the 350.7‐nm line of a krypton ion laser. In addition we present the accompanying fluorescence spectrum which shows previously unreported discrete structure on the short wavelength side of the violet bands.

New measurements of the a3 Σ+u state of K2 and improved analysis of long‐range dispersion and exchange interactions between two K atoms

Resolved fluorescence from the K2 43 Σ+g state to the a3 Σ+u state has been measured by the perturbation‐facilitated optical–optical double resonance (PFOODR) technique. Data have been fit to an improved set of molecular constants for the a3 Σ+u state. In particular, the new Te value for this state has been determined as 4197.935±0.047 cm−1, nearly 1.8 cm−1 higher than previously reported. By combining the new results for the a3 Σ+u state and the recent results for the ground X1 Σ+g state [J. Chem. Phys. 103, 3350 (1995)], we report in this paper an improved analysis of long‐range dispersion and exchange interactions between two K atoms and of the X1 Σ+g and a3 Σ+u state dissociation energies De of 4450.674±0.072 cm−1 and 252.74±0.12 cm−1, respectively.

Perturbation facilitated optical–optical double resonance spectroscopy of the 2 3Σ+g, 3 3Σ+g, and 4 3Σ+g Rydberg states of 7Li2

This paper reports the experimental observation of the 2 3Σ+g, 3 3Σ+g, and 4 3Σ+g states of 7Li2 by cw perturbation facilitated optical–optical double resonance spectroscopy. Molecular constants and RKR potential curves have been obtained. Our experimental Te and Re for the 2 3Σ+g state are 27 297.45(16) cm−1 and 3.0797(18) A, respectively, and for the 3 3Σ+g state are 31 043.93(53) cm−1 and 3.0378(19) A, respectively. The above values are in very good agreement with theoretical calculations. Hyperfine splitting for both states has been resolved. Both states follow Hund’s case (bβS) hyperfine coupling scheme. The experimental Fermi contact parameter, bF, is approximately 96±2 MHz for the 2 3Σ+g state and 95.6±3 MHz for the 3 3Σ+g state. These values are in good agreement with the previously obtained value 98.6±4 MHz [Li et al., J. Chem. Phys. 96, 3342 (1992)]. One level of the 4 3Σ+g state has been observed and its hyperfine structure has been resolved and characterized with Hund’s coupling case (bβS).

Direct excitation studies of the diffuse bands of alkali metal dimers

Direct dye laser excitations of the K2 yellow, Rb2 orange, and Cs2 near‐infrared diffuse bands have been investigated. Experimental results are shown to be consistent with the assumed bound–free 2 3Πg–1 3∑+u excitations. It is found that for Rb2 and Cs2, spin–orbit interactions become so significant that the 2 3Πg state is strongly split into three quite independent component states.

Observation of the 4 3Σ+g, 3 3Πg, 2 3Δg, and b 3Πu states of 39K2 by perturbation facilitated optical–optical double resonance spectroscopy

The 4 3Σ+g, 3 3Πg, and 2 3Δg states of K2 have been studied by perturbation facilitated optical–optical double resonance spectroscopy for the first time. Molecular constants of those states are derived and compared with theoretical calculations. Varying the trial vibrational quantum numbers of these upper states, absolute vibrational quantum number assignments are obtained by comparison between the observed resolved fluorescence intensities and the calculated Franck–Condon factors. The Rydberg–Klein–Rees potential curves are constructed and compared with theoretical calculations. Finally, the observation of the lowest ‘‘dark’’ vibrational levels of the b 3Πu state by resolved fluorescence from the 2 3Δg state confirmed the absolute vibrational numbering of this state and allowed refinement of the b 3Πu molecular constants.

Determination of the long-range potential and dissociation energy of the 1 3Δg state of Na2

The 1 3Δg state of Na2 has been studied extensively by both filtered fluorescence and ionization detection and analyzed by both Dunham‐type expansion and near‐dissociation expansion (NDE) models in the analysis. Our observations have covered 99.998% of the potential well depth with the outermost Rydberg–Klein–Rees (RKR) turning point at 28.02 A. NDE analysis gives Te=28 032.468 (±0.021) cm−1, De=7162.436 (±0.021) cm−1, and Re=3.463 81 (±0.000 28) A. Significant long‐range behavior in the near dissociation levels has been observed. Fitting of the RKR turning points gives the long‐range coefficients C5=1.388 (±0.031)×106 cm−1 A5 and C6=0.4008 (±0.0046)×108 cm−1 A6. These newly observed results show reasonable agreement with recent theoretical calculations.