Condon Internal Diffraction Research Articles

LIF dispersed emission spectra and characterization of ZnRg (Rg = Ne, Ar, Kr) ground-state potentials

Laser-induced fluorescence dispersed emission spectra recorded using the C 1 Π 1 ( υ ′ ) → X 1 Σ 0 + transition in ZnKr, ZnAr and ZnNe complexes are reported. The complexes were produced in a continuous free-jet beam crossed with a pulsed dye-laser beam. The spectra were recorded using a spectrograph equipped with CCD camera. The recorded profiles displayed characteristic Condon internal diffraction patterns. The patterns consisted of reflection type continuous features corresponding to bound → free transitions and bound → bound transitions. In simulation of the spectra, M–S(9.09, 7.81), M–S(10.86, 10.32) and M–S(14.49, 8.91) Maitland–Smith M–S( n 0, n 1) functions were found to represent the repulsive walls of the X 1 Σ 0 + -state potentials of ZnKr, ZnAr and ZnNe, respectively. The obtained results were compared with available experimental and theoretical representations of other studies.

Potential energy curves for the B11u state and short-range part of the X10+g state of Cd2 determined from excitation and dispersed fluorescence spectra recorded using the B11u ↔ X10+g transition

Laser-induced fluorescence excitation and dispersed fluorescence spectra of a cadmium dimer recorded using the B11u ↔ X10+g transition are reported. In the excitation, well-resolved isotopic structure of several υ′ ← υ″ = 0 vibrational components (υ′ from 34 to 40) as well as a free ← bound unstructured band was recorded. The B11u-state interatomic potential was derived using the ‘inverse-perturbation’ fitting method. In the dispersed fluorescence after selective excitation of the B-state υ′ = 39 level of the 226Cd2 molecular isotopic component, a Condon internal diffraction pattern was recorded and simulated, confirming the υ′-assignment. Analysis of the dispersed fluorescence spectrum yielded information on the repulsive branch of the ground-state potential. The experimental results were compared with results of ab initio calculations as well as with experimental results of earlier studies.

Group-12 vdW dimers in free-jet supersonic beams: The legacy of Eugeniusz Czuchaj continues

Laser induced excitation and dispersed fluorescence spectra of group-12 metal homoatomic dimers (Zn 2 , Cd 2, Hg 2 ) recorded at a number of ultraviolet transitions provided information about interatomic potentials of the ground and lower-lying excited electron energy states of the dimers. The experimental studies were associated with calculations performed by Eugeniusz Czuchaj that were related to interatomic potentials as well as dipole moments for transitions between the ground and the excited states of the dimers. In experiments the dimers were produced in free-jet supersonic beams and were excited in a vacuum chamber with dye-laser beams. Isotopically resolved vibrational transitions in low-resolution excitation spectra and high-resolution rotational profiles of several vibrational components as well as Condon internal diffraction patterns in dispersed fluorescence spectra were recorded. Complex analyses of the spectra yielded information about the ground- and excited-state potential bond lengths, well depths as well as shapes of the investigated potentials in limited regions of internuclear separations. The determined potential energy curves were compared with results of Czuchaj providing conclusions related to the accuracy of calculations and/or experiments as well as giving the experimentalist information about planning experimental studies of molecular potentials of the group-12 dimers.

Spectroscopy of the 11 u(5 1P 1) and [formula omitted] singlet electronic states of cadmium dimer: Bond lengths and verification of ab initio potentials

A method of supersonic free-jet expansion beam combined with techniques of laser spectroscopy was used in investigation of vibrational and rotational structures in the 1 0 u + ( 5 1 P 1 ) and 11 u(5 1P 1) electronic energy states of Cd 2. Laser induced fluorescence (LIF) excitation and dispersed fluorescence spectra recorded at the 1 0 u + - X 1 0 g + and 1 1 u - X 1 0 g + transitions provided spectroscopic characteristics of the excited and ground states as well as a shape of the repulsive part of the ground-state potential energy curve (PEC). Rotational structures of the 228Cd 2 isotopomer recorded in the ( υ′, υ″) = (45,0) and (38,0) bands of the 1 0 u + ← X 1 0 g + and 1 1 u ← X 1 0 g + transitions, respectively, were used for a direct determination of the ground- and excited-state bond lengths. Moreover, the 11 u-state interatomic potential was obtained numerically using an inverted perturbation approach (IPA). The position and height of the 11 u-state potential barrier was determined and compared with results of ab initio calculation. Analysis of Condon-internal-diffraction (CID) profiles in the bound-free dispersed fluorescence spectrum resulted in determination of a degree of repulsion between two ground-state Cd atoms in the dimer, supporting a hypothesis of a covalent admixture to the dominant van der Waals (vdW) bonding.

Structure of excitation and fluorescence spectra recorded at the10u+(51P1)–X10g+transition ofCd2

Excitation and fluorescence ultraviolet spectra of ${\mathrm{Cd}}_{2}$ recorded at the ${}^{1}{0}_{u}^{+}(5{}^{1}{P}_{1})--X{}^{1}{0}_{g}^{+}$ transition are reported. The ${\mathrm{Cd}}_{2}$ molecules (seeded in Ar) produced in a continuous free-jet supersonic beam were excited in a vacuum chamber with a pulsed dye-laser beam. A well-resolved vibrational structure of the ${}^{1}{0}_{u}^{+}\ensuremath{\leftarrow}X{}^{1}{0}_{g}^{+}$ excitation spectrum as well as the isotopic structure of the vibrational components were recorded. Analysis of the spectrum yielded vibrational constants for the ${}^{1}{0}_{u}^{+}$ state: ${\ensuremath{\omega}}_{e}^{\ensuremath{'}}=100.50\ifmmode\pm\else\textpm\fi{}0.25{\mathrm{cm}}^{\ensuremath{-}1},$ ${\ensuremath{\omega}}_{e}^{\ensuremath{'}}{x}_{e}^{\ensuremath{'}}=0.325\ifmmode\pm\else\textpm\fi{}0.003{\mathrm{cm}}^{\ensuremath{-}1},$ ${D}_{0}^{\ensuremath{'}}=8638\ifmmode\pm\else\textpm\fi{}15{\mathrm{cm}}^{\ensuremath{-}1},$ ${D}_{e}^{\ensuremath{'}}=8688\ifmmode\pm\else\textpm\fi{}15{\mathrm{cm}}^{\ensuremath{-}1},$ and $\ensuremath{\Delta}{R}_{e}{=R}_{e}^{\ensuremath{''}}\ensuremath{-}{R}_{e}^{\ensuremath{'}}=1.04\ifmmode\pm\else\textpm\fi{}0.01\AA{}$ derived for the ${}^{226}{\mathrm{Cd}}_{2}$ isotopomer. The ${}^{1}{0}_{u}^{+}$ state potential-energy (PE) curve was obtained numerically using an inverse perturbation approach (IPA) procedure. Condon internal diffraction (CID) patterns in the ${}^{1}{0}_{u}^{+}\ensuremath{\rightarrow}X{}^{1}{0}_{g}^{+}$ fluorescence band, emitted upon the selective excitation of the ${v}^{\ensuremath{'}}=38$ and ${v}^{\ensuremath{'}}=39$ vibrational components of the ${}^{226}{\mathrm{Cd}}_{2}$ isotopomer, were observed and improved the ${v}^{\ensuremath{'}}$ assignments derived from the analysis of the isotopic structure. Analysis of the fluorescence spectrum yielded information on the repulsive part of the ground-state interatomic potential. The result confirms a relatively soft repulsion between two Cd atoms in the short-range (2.53--4.05 \AA{}) region and makes allowance for a covalent admixture to the ground-state van der Waals bonding. Quasirelativistic valence ab initio calculations on the PE curves for the investigated states have been performed at the complete-active-space multiconfiguration self-consistent-field (CASSCF/CAS) multireference second-order perturbation theory (CASPT2) level with the total of 40 correlated electrons. In the calculations, the Cd atom is considered as a 20-valence electron system whereas the ${\mathrm{Cd}}^{20+}$ core is replaced by an energy-consistent pseudopotential which also accounts for scalar-relativistic effects and spin-orbit interaction within the valence shell. A comparison with results obtained from other experiments and ab initio calculations is presented.

Short-Range Characterization of the MeAr (Me=Zn, Cd) Ground-State Potentials from Fluorescence Spectra

First-time observed D1(1Π)v′=10→X0+(1Σ) fluorescence in ZnAr, and A0+(3Π)v′=4→X0+ and D1(1Π)v′=7,8→X0+ fluorescence in CdAr van der Waals (vdW) molecules were produced in a continuous supersonic molecular beam crossed with a pulsed dye-laser beam, following excitation of single vibronic levels. The dispersed fluorescence spectra displayed characteristic Condon internal diffraction (CID) patterns consisting of bound–free, reflection type, continuous spectra, and, in certain cases, bound–bound discrete features. An analysis of the A0+→X0+ and D1→X0+ bound–bound spectra indicates that Morse functions are adequate representations of the X0+ potential energy (PE) curves below their dissociation limits. In simulation of the A0+→X0+ and D1→X0+ bound–free spectra, the Morse, Lennard–Jones L–J(n−6), and Maitland–Smith M–S(n0,n1) functions were tested, and the respective M–S(11.3, 9.0) and M–S(10.6, 7.0) potentials were found to be good representations for the repulsive walls of the X0+ PE curves of ZnAr and CdAr, respectively, over the short range, R=2.45–4.38 Å (ZnAr) and R=2.85–4.31 Å (CdAr), of internuclear separations.

TheG0u+(61P1)–X0G+Excitation and Fluorescence Spectra of Hg2Excited in a Supersonic Jet

TheG0u+(61P1)–X0G+excitation and fluorescence spectra of Hg2van der Waals molecules, produced in a pulsed free-jet supersonic expansion beam crossed with a pulsed dye-laser beam, were studied using Ar as the carrier gas. A well-resolved vibrational structure of theG0u+←X0g+excitation spectrum was recorded, as well as the isotopic structures of the vibrational components. A Condon internal diffraction pattern in theG0u+→X0g+fluorescence band, emitted upon the selective excitation of the v′ = 39 vibrational component, was also observed and confirmed the assignments derived from the analysis of the isotopic structure. Analyses of the spectra yielded molecular constants for both states, as well as information on the ground state potential energy curve. The results are compared with those obtained from other experiments and from theoretical calculations.

Two-colour photoassociation spectroscopy of ultracold sodium

We demonstrate a number of two-colour spectroscopy techniques where the first step is the photoassociation of laser-cooled and trapped sodium atoms to form bound states of . High-resolution spectra of are obtained. Spectra of the `purely long-range' state demonstrates the use of two-colour spectroscopy to open up an ionization channel for detecting the occurrence of photoassociation. The utility of photoassociation as a technique for producing cold molecular samples in a well defined rovibrational state is demonstrated with spectra showing and (Condon internal diffraction) transitions after the photoassociation. Starting from states in the and potentials, these transitions include upward transitions to autoionizing potentials dissociating near 3P + 3P and downward transitions back to the 3S + 3S ground-state potentials. Spectroscopic constants for six levels of a doubly excited state of are given.

Potential energy curve of the ground state of HgAr determined from fluorescence spectra

Abstract A 0 + ( 3 Π) → X 0 + ( 1 Σ + ) and B 1( 3 Σ + ) → X 0 + ( 1 Σ + ) fluorescence spectra of HgAr van der Waals molecules were previously produced in a pulsed supersonic molecular beam crossed with a pulsed dye-laser beam, following excitation of single vibronic levels. The dispersed fluorescence displayed characteristic Condon internal diffraction (CID) patterns consisting of bound-free reflection type, continuous spectra, and also bound-bound discrete features. An analysis of the AO+ → X0+ and B1 → XO+ bound-bound spectra indicates that a Morese function is an adequate representatation of the X0+ potential energy (PE) curve below the dissociation limit. In simulation of the AO+ → X0+ bound-free spectra of the Morse, Lennard-Jones (n − 6) and Maitland-Smith functions were tested, and the Maitland-Smith potential was found to be a good representation of the repulsive wall of the X0+ PE curve above the dissociation limit over the internuclear separation range R = 2.8–3.5 A .

Laser excitation spectroscopy of the B 1Σ+u(O+u)←a 3Πg(O+g) transition of Cd2: Vibrational analysis and rotational structure

The B 1Σ+u←a 3Πg transition of Cd2 (natural abundance) and 114Cd2 has been observed by laser excitation spectroscopy and analyzed. By exciting the Cd2 B←a transition in the visible (560≤λ≤730 nm) while monitoring B 1Σ+u→X 1Σ+g (bound→free) emission in the ultraviolet (∼270–310 nm), more than 40 red-degraded vibrational bands were recorded. Analysis of the spectrum has yielded vibrational constants for both the a 3Πg and B 1Σ+u states: ωe″=153.6±4.0 cm−1, ωe″xe″=0.52±0.06 cm−1, ωe′=105.3±1.0 cm−1, and ωe′xe′=0.44±0.03 cm−1. In addition, ΔRe≡ReB−Rea was determined to be 0.31±0.03 Å. Rotational structure has been partially resolved for 114Cd2 bands in the 620–655 nm and 719–723 nm regions, and the spontaneous emission lifetime of the a 3Πg state and the rate constant for quenching of Cd2 (a 3Πg) by collisions with background Cd atoms have been determined to be 8.6±2.5 μs and (2.2±0.3)×10−13 cm3 s−1, respectively. Also, analysis of the B→X emission (Condon internal diffraction) spectra produced when specific B 1Σ+u vibrational levels are populated has yielded ReX−ReB=0.95±0.02 Å.

Spectroscopy of the A0+ and B1 states in HgAr and HgNe

Excitation spectra of HgNe and HgAr van der Waals molecules were produced in a pulsed supersonic molecular beam crossed with a pulsed dye-laser beam. Bands arising from A0+ ← X0+ and B1 ← X0+ vibronic transitions were analyzed, yielding spectroscopic constants for HgNe and HgAr. A0+ → X0+ and B1 → X0+ fluorescence spectra of HgAr were also recorded, consisting of Condon internal diffraction patterns arising from bound-free decays of various vibronic states, together with vibrational components produced by bound-bound transitions. Term analyses of the spectra combined with computer-modeling calculations produced improved values of spectroscopic constants.

Laser spectroscopy of the 1Σ +u (4 1P) and 3Π u (4 3P) states in Zn 2

The 0 + u (4 1P) state of Zn 2 was excited near the crossing of the 1Σ + u (4 1P) and 3Π u (4 3P) states, using pump and probe methods with time resolution. A structured excitation spectrum was observed in the 530–570 nm region and is ascribed to the 3Π u(4 3P)← 3Π g(4 3P) vibronic transitions. A fluorescence spectrum which was emitted in the 250–306 nm region is believed to arise from the 1Σ + u→X 1Σ + g bound—free decay. It consists of a “Condon internal diffraction pattern” whose profile suggests that it was emitted from a high vibrational level ( v′ = 19) of the 1Σ + u state.

Laser-induced fluorescence of Hg2 H1u excimer molecules.

Vibrational levels of the H${1}_{u}$ state in ${\mathrm{Hg}}_{2}$ excimer molecules, correlated with the 6? sup 1 P sub 1--- atomic state, were selectively populated by stepwise excitation using the metastable A${0}_{g}^{\ifmmode\pm\else\textpm\fi{}}$ states for the intermediate step, and the fluorescence emitted in the H${1}_{u}$\ensuremath{\rightarrow}X${0}_{g}^{+}$ bound-free decay was recorded with a spectrometer and a transient digitizer. The uv fluorescence bands, emitted in the decay of several upper-state vibrational levels with v' ranging from 0 to 5, were centered near 1994 A\r{} and consisted of well-resolved Condon internal diffraction patterns corresponding to appropriate upper-state vibrational wave functions. The energy separation between the A${0}_{g}^{\ifmmode\pm\else\textpm\fi{}}$ and H${1}_{u}$ potential minima was determined and an estimate was made of the vibrational frequency ${\ensuremath{\omega}}_{e}$ of the H${1}_{u}$ state. Much weaker excitation of the H${1}_{u}$ state was also effected from the metastable B${1}_{g}$ state, which allowed the energy separation between the B${1}_{g}$ and A${0}_{g}^{\ifmmode\pm\else\textpm\fi{}}$ potential minima to be determined experimentally.

Sub-Doppler laser spectroscopy of the NaK molecule

Excitation of NaK molecules in a collimated molecular beam by a single mode tunable argon laser with sub-Doppler resolution allows selective population of definite vibrational rotational levels (v′, J′) in the D 1Π-state. The resultant fluorescence consists of a singlet spectrum in the 470–570 nm range and a triplet spectrum in the 625–715 nm range. The analysis of the triplet fluorescence, which consists of discrete lines and of a modulated continuum, allows the determination of the a 3Σ+ potential and yields very precise values for the dissociation energies in the a 3Σ+ and X 1Σ+ states, which are measured as De(3Σ+) =204±4 cm−1 and De(1Σ+) =5269±6 cm−1. For some excitation wavelengths a fluorescence spectrum with discrete lines and with a double-modulated continuum is observed which is assigned to ’’ Condon internal diffraction’’ bands terminating close below and above the dissociation limit of the X 1Σ+ state. Its relevance for the determination of the upper and lower potential curves is discussed.