F. Engelke

Laser induced fluorescence spectroscopy of NaLi in beam and bulk

Abstract The laser induced fluorescence spectra of Na 6 Li and Na 7 Li formed (a) in a nozzle beam using a newly designed three-chamber oven and (b) in an injection heat pipe have been measured and analysed. The assignment of one series, first obtained by Hessel in 1971, has been revised and many new resonance series observed. Corrected vibrational and rotational constants and the RKR curves for both the ground X 1 Σ + and the excited B 1 Π states are reported. The long-range part of the X state potential is investigated and a C 6 constant as well as precise dissociation energies for both states are obtained. Comparison is made with the predictions of ab initio and pseudopotential calculations, which agree to within 4% for the ground state, but not for the excited state.

Rotational polarization of product molecules: Crossed laser-molecular-beam studies of Ca* + HF and Ca + F2

Abstract Laser-induced fluorescence (LIF) is used to probe the spatial polarization of nascent CaF reaction products. The results give direct information on the role of angular momentum alignment of CaF in Ca*( 3 P 1,2,3 ) + HF and Ca( 1 S o ) + F 2 , reactive scattering.

The K2 B1Πu-X1Σ+g band system. Crossed laser-molecular-beam spectroscopy using doppler-free two-photon ionization

Abstract Two-photon-ionization spectra of 39 K 2 . 39 K 41 K and 41 K 2 formed in a nozzle beam have been measured and analysed. The assignment of B 1 Π u -X 1 Σ g + has been revised. Correct vibrational and rotational constants for both the ground X 1 Σ g + and the excited B 1 Π u states are reported.

First observation of hyperfine structure of the 23Na39K c3Σ+ state

Abstract The c 3 Σ + state of 23 Na 39 K has been observed and partly analyzed for the first time from crossed laser-molecular beam spectroscopy. The 23 Na nuclear hyperfine structure is dominating and typically spread over more than 1000 MHz. The observed patterns are discussed in terms of the electronic structure of the c 3 Σ + state.

A theoretical and experimental investigation of the predissociative line shifts of the b 3Πu state of Li2

Abstract Line shifts of rovibrational levels of the state of the b 3 Π u state of Li 2 caused by rotational coupling to the a 3 Σ u + state have been determined both theoretically and experimentally. Calculated and empirical unshifted term values of the b 3 Π u state are found to be in excellent agreement. The calculated line shifts show the expected oscillatory structure and agree with the experimental data. Using the shifted b 3 Π u energy levels and applying a minor modification to the ab initio a 3 Σ u + potential curve as indicated by comparison with experimental line widths, theoretical accidental predissociation lifetimes of the Li 2 A 1 Σ u + state are obtained in almost perfect agreement with the measured values.

The injection heat pipe (IHP). A new device for spectroscopic studies using laser-induced fluorescence (LIF): Operation and spectroscopic applications

Abstract The injection heat pipe (IHP), a new device based on the well-known heat-pipe oven, has been demonstrated to be extraordinarily useful in laser-induced-fluorescence (LIF) studies of different mixed metal molecules. The IHP allows fluorescence studies under known, uniform and easily adjustable metal compound concentrations even for immiscible metals. For a given temperature of the heat-pipe operation, fluorescence intensity is approximately two orders of magnitude more intense than in a traditional crossed heat pipe. Experimental aspects, analysis of the injection process, and general applications of the IHP are discussed. Detailed studies of mixed alkali dimers MM′ (M: 6 Li, 7 Li; M′: Na, K, Rb, Cs) are presented. The great impact of laser spectroscopy in the field of inelastic collisions of electronically excited molecules is illustrated by a few selected examples: NaLi * , BaX * + A, where X = F, Cl, Br, and A = He, Ne, Ar, and Kr, including the measurements of rotational, vibrational-rotational and even intra-multiplet energy-transfer processes.

cw Two-photon transitions in K2 molecular beams

Abstract We report on the two-photon visible excitation spectra of potassium molecules in a supersonic beam. A dye laser excites K 2 to different (7s 1 Σ g , 9s 1 Σ g , 8d 1 Δ g ) Rydberg states. Two-photon transitions are detected by monitoring the resulting (third-photon) ionization. We have made detailed studies, including rotational assignment of 92 such transitions, 1 Δ g ( v ∗ , J ∗ ) ← X 1 Σ g ( v = 0, J ), where the B 1 Π u state forms the intermediate enhancing state.

Rydberg states of the K2 molecule studied by laser spectroscopy in a supersonic beam

Rydberg states of potassium dimer have been studied in a crossed laser-molecular beam experiment. The K2 molecules were formed in a supersonic expansion and excited by low-power cw dye laser. Two different excitation schemes have been used: The first scheme uses a single mode ring dye laser to induce near resonant two-photon transitions while in the second scheme stepwise excitation with two dye lasers is used. In each case excitation of Rydberg levels was detected by monitoring the ionization signal resulting from three-photon absorption. We report a detailed study of 700 two-photon resonances between 625 nm and 650 nm. Most of these signals can be assigned to transitions from the X1σg+ to1σg+,1Πg, and1Δg states, which are all enhanced by the B1Πu intermediate state. Accurate rotational constants are given for the populated vibrational levels of these states. By stepwise excitation of Rydberg levels via theB1Πu state we identify 3 series of Rydberg states as1Δg (4S+nD),1Σg+ (4S+nD), and1Σg+ (4S+nS) with principal quantum numbers 7≦n≦20. Molecular constants of these and other observed but as yet unidentified states are given; quantum defects and dissociation energies are discussed.

Observation and characterization of a doubly excited electronic state of 39K2

Abstract Supersonic nozzle beam and optical-optical double resonance techniques using a cw single-mode ring dye laser as a pump and a narrow-band pulsed dye laser as a probe have been used to make the first spectroscopic study of a doubly excited electronic state ( 1 Σ g − ) of 39 K 2 above the (lowest) 2 Σ g + state of K 2 + . Molecular constants (in cm −1 ) are T e = 36599.7(1), ω e = 43.47(3), ω e χ e = 0.225 (3), B e = 0.0444(3), α e = 0.00027 (5), and R e = 4.41 A.

Laser studies of reaction dynamics

Laser and molecular beam techniques allow detailed study of many dynamical properties of single reactive collisions. The chemical scope of these methods is now very wide and includes internal state preparation of reactants, change of collision energies, state detection of products, and thus determination of state-to-state reaction rates. The great impact of laser spectroscopy on knowledge in the field of structure, molecular energy transfer and the mechanism of elementary chemical reactions is illustrated by a few selected examples, including studies in which laser-induced fluorescence (LIF) has been used to to determine the polarization of reaction products