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Photoassociation of krypton and fluorine collision pairs

J. H. Schloss

Published Jan 1, 1989• 0 citations
OpenAlex

Abstract

The photoassociation spectrum of Kr-F collision pairs in thermal equilibrium (293$\sp\circ$K) to KrF(B) has been observed using a laser-induced fluorescence technique with a tunable probe over the wavelength range 219 nm $\leq$ $\lambda$ $\leq$ 250 nm. The spectrum was then analyzed by numerical calculation of the Franck-Condon factors for the bound $\gets$ free transitions. The numerical calculation provided information on the KrF(X) and KrF(B) potential as well as the KrF(B $\to$ X) electronic dipole moment. Saturation intensities for photoassociation produced population were determined at 248 nm for gas mixtures with Kr partial pressures in the range 125 Torr $\leq$ p$\sb{\rm Kr}$ $\leq$ 1000 Torr and 1 Torr of F$\sb2$. Two-photon absorption of Kr/F$\sb2$ mixtures was also observed over the wavelength range 220 nm $\leq$ $\lambda$ $\leq$ 250 nm. The mechanism of the two-photon absorption is determined to be photodissociation of F$\sb2$ followed by photoassociation of non-thermalized Kr-F collision pairs.

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Excitation spectra for the photoassociation of Kr–F and Xe–I collision pairs in the ultraviolet (208–258 nm)

R. B. Jones, J. H. Schloss, James Gary Eden

Photoassociation, the bound←free absorption of a photon by a colliding pair of atoms, has been studied experimentally in the Kr–F and Xe–I systems and is demonstrated to be an effective tool for deducing molecular interaction potentials and for determining the dependence of the relative electronic transition moment on internuclear separation (R) in small molecules having dissociative ground states. Specifically, the excitation (‘‘action’’) spectrum for the photoassociation of thermalized Kr(4p6 1S0)–F(2p5 2P) collision pairs, measured at 300 K in the 208–250 nm wavelength region, reveals deeply modulated Franck–Condon structure associated with transitions of Kr–F pairs from the ground state’s thermal and vibrational continua to the lowest 27 bound vibrational states (v′=0–26) of the KrF(B 2Σ) excited state. Under these conditions, photoassociation occurs in a narrow (ΔR=0.7–0.8 Å) Franck–Condon region in which the difference potential is a single valued function of R. Similar spectra have been observed for Xe(1S0)–I(2P) pairs in the 208–258 nm spectral region that arise from bound←free transitions to the lowest ∼40 vibrational levels of the XeI(B) state. Since the Kr–F and Xe–I collision pairs are photoexcited from the vibrational continuum of the ground state, the atomic pair energy distribution is thermalized and the envelope of the excitation spectrum can be interpreted directly in terms of the relative B–X transition moment, μ(R). Consequently, the behavior of μ(R) has been determined over a limited range in R and, for XeI, μ is found to fall by a factor of 2 in the ∼0.4 Å region extending from R−ReB≊0.25–0.62 Å. The XeI ground state (X 2Σ1/2+) potential in the 3.0≤R≤5.0 Å interval, derived from photoassociation spectra, is similar to that deduced from scattering experiments. Excited and ground state structural constants derived from numerical quantum simulations of the experimental spectra are presented.

The Journal of Chemical Physics•Mar 15, 1993•37 citations

Cs 8943 nm laser pumped by photoassociation of Cs-Kr pairs: excitation of the Cs D_2 blue and red satellites

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Lasing on the D(1) transition (6P1/22-->6S1/22) of Cs has been observed by photoassociating Cs-Kr atomic pairs with a tunable, pulsed dye laser. Pumping of the blue or red satellites of the Cs D(2) line (62P3/2<==>62S1/2), peaking at approximately 841.1 nm and approximately 853 nm (respectively) in Cs/Kr/C(2)H(6) gas mixtures, provides a photodissociation laser in which the CsKr excimer parent molecule is not, at any point in the pumping process, in a bound electronic state. Relative to the absorbed pump pulse energy, laser slope efficiencies greater than or approximately 5% have been measured when the Cs number density is in the range of 5x10(14)-1.5x10(15) cm(-3) and the pump wavelength is 841.1 nm. Direct photoexcitation of the Cs 6P3/22 state at 852.1 nm under these conditions is a less efficient pathway for pumping the 894.3 nm laser, presumably as a result of competing nonlinear optical processes such as 1+2 resonantly enhanced multiphoton ionization of the alkali atom.

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Photoassociation spectroscopy

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Cambridge University Press eBooks•Dec 4, 2003•0 citations

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•Jan 1, 1998•0 citations

Purely-long-range krypton molecules in singly and doubly excited binding potentials

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Diatomic potentials for krypton are computed and also probed experimentally. For a probe-laser wavelength near $811$ nm, several strong dipole-dipole interactions produce purely-long-range potential wells in the singly excited manifold of ($s+p$) potentials and in the doubly excited manifold of ($p+p$) and ($s+d$) potentials. Evidence of resonant photoassociation into bound states of these potential wells is observed in the emission of ions and ultraviolet photons from a magneto-optically trapped krypton cloud.

Physical Review A•Jan 14, 2010•6 citations

LASER SPECTROSCOPY OF THE PHOTOASSOCIATION OF Rb-Ar AND Rb-Kr THERMAL PAIRS: STRUCTURE OF THE Rb-RARE GAS A2_1/2 STATE NEAR THE CLASSICAL LIMIT

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A new laser spectroscopic technique has been demonstrated for examining the structure of alkali--rare gas diatomic electronic states near the classical limit. In two-color experiments, Rb--Ar or Rb--Kr thermal pairs are excited by free$leftarrow$free or bound$leftarrow$free transitions while monitoring the amplified spontaneous emission produced on the Rb D$_1$ or D$_2$ lines. Spectra observed lying within 10 cm$^{-1}$ of the separated atom limit for the A$^{2}Pi_{1/2}$ states of Rb--Ar and Rb--Kr will be presented and discussed.

•Jan 5, 2016•0 citations
The photoassociation spectrum of Kr-F collision pairs in thermal equilibrium (293\sp∘\sp\circ\sp∘K) to KrF(B) has been observed using a laser-induced fluorescence technique with a tunable probe over the wavelength range 219 nm ≤\leq≤ λ\lambdaλ ≤\leq≤ 250 nm. The spectrum was then analyzed by numerical calculation of the Franck-Condon factors for the bound ←\gets← free transitions. The numerical calculation provided information on the KrF(X) and KrF(B) potential as well as the KrF(B →\to→ X) electronic dipole moment. Saturation intensities for photoassociation produced population were determined at 248 nm for gas mixtures with Kr partial pressures in the range 125 Torr ≤\leq≤ p\sbKr\sb{\rm Kr}\sbKr ≤\leq≤ 1000 Torr and 1 Torr of F\sb2\sb2\sb2. Two-photon absorption of Kr/F\sb2\sb2\sb2 mixtures was also observed over the wavelength range 220 nm ≤\leq≤ λ\lambdaλ ≤\leq≤ 250 nm. The mechanism of the two-photon absorption is determined to be photodissociation of F\sb2\sb2\sb2 followed by photoassociation of non-thermalized Kr-F collision pairs.
Photoassociation, the bound←free absorption of a photon by a colliding pair of atoms, has been studied experimentally in the Kr–F and Xe–I systems and is demonstrated to be an effective tool for deducing molecular interaction potentials and for determining the dependence of the relative electronic transition moment on internuclear separation (R) in small molecules having dissociative ground states. Specifically, the excitation (‘‘action’’) spectrum for the photoassociation of thermalized Kr(4p6 1S0)–F(2p5 2P) collision pairs, measured at 300 K in the 208–250 nm wavelength region, reveals deeply modulated Franck–Condon structure associated with transitions of Kr–F pairs from the ground state’s thermal and vibrational continua to the lowest 27 bound vibrational states (v′=0–26) of the KrF(B 2Σ) excited state. Under these conditions, photoassociation occurs in a narrow (ΔR=0.7–0.8 Å) Franck–Condon region in which the difference potential is a single valued function of R. Similar spectra have been observed for Xe(1S0)–I(2P) pairs in the 208–258 nm spectral region that arise from bound←free transitions to the lowest ∼40 vibrational levels of the XeI(B) state. Since the Kr–F and Xe–I collision pairs are photoexcited from the vibrational continuum of the ground state, the atomic pair energy distribution is thermalized and the envelope of the excitation spectrum can be interpreted directly in terms of the relative B–X transition moment, μ(R). Consequently, the behavior of μ(R) has been determined over a limited range in R and, for XeI, μ is found to fall by a factor of 2 in the ∼0.4 Å region extending from R−ReB≊0.25–0.62 Å. The XeI ground state (X 2Σ1/2+) potential in the 3.0≤R≤5.0 Å interval, derived from photoassociation spectra, is similar to that deduced from scattering experiments. Excited and ground state structural constants derived from numerical quantum simulations of the experimental spectra are presented.
Lasing on the D(1) transition (6P1/22-->6S1/22) of Cs has been observed by photoassociating Cs-Kr atomic pairs with a tunable, pulsed dye laser. Pumping of the blue or red satellites of the Cs D(2) line (62P3/2<==>62S1/2), peaking at approximately 841.1 nm and approximately 853 nm (respectively) in Cs/Kr/C(2)H(6) gas mixtures, provides a photodissociation laser in which the CsKr excimer parent molecule is not, at any point in the pumping process, in a bound electronic state. Relative to the absorbed pump pulse energy, laser slope efficiencies greater than or approximately 5% have been measured when the Cs number density is in the range of 5x10(14)-1.5x10(15) cm(-3) and the pump wavelength is 841.1 nm. Direct photoexcitation of the Cs 6P3/22 state at 852.1 nm under these conditions is a less efficient pathway for pumping the 894.3 nm laser, presumably as a result of competing nonlinear optical processes such as 1+2 resonantly enhanced multiphoton ionization of the alkali atom.
Introduction If, while approaching on an unbound ground-state potential, two atoms absorb a photon and couple to an excited bound molecular state, they are said to undergo photoassociation. Figure 5.1 illustrates the process. At long range electrostatic dispersion forces give rise to the ground-state molecular potential varying as C 6 / R 6 . If the two atoms are homonuclear, then a resonant dipole–dipole interaction sets up ± C 3 / R 3 excited-state repulsive and attractive potentials. Figure 5.2 shows the actual long-range excited potential curves for the sodium dimer, originating from the 2 S ½ + 2 P 3/2 and 2 S ½ + 2 P ½ separated atom states. For cold and ultracold photoassociation processes the long-range attractive potentials play the key role; the repulsive potentials figure importantly in optical shielding and suppression, the subject of Chapter 6. In the presence of a photon with frequency ω p the colliding pair with kinetic energy k B T couples from the ground-state to the attractive molecular state in a free–bound transition near the Condon point R C , the point at which the difference potential just matches ћω p . Scanning the probe laser ω p excites population of vibration–rotation states in the excited bound potential and generates a free–bound spectrum. This general class of measurements is called photoassociative spectroscopy (PAS) and can be observed in several different ways. The observation may consist of bound-state decay by spontaneous emission, most probably as the nuclei move slowly around the outer turning point, to some distribution of continuum states on the ground potential controlled by bound–free nuclear Franck–Condon overlap factors.
The field of laser cooling and trapping of atoms has had a profound impact on many areas of atomic, molecular and optical science. In particular, ultracold atoms colliding in magneto-optical traps typically have relative kinetic energies of 300muK(sim7MHz)300\\mu K (\\sim 7 MHz)300muK(sim7MHz), so free-bound absorption lines are as sharp as bound-bound lines. Moreover, because of very long range centrifugal barriers, only a few collisional partial waves are important (Jprimeprime=0,1J^{\\prime\\prime} = 0, 1Jprimeprime=0,1 and 2 in our work on 39K^{39}K39K). Such photoassociative free-bound absorption allows observation of ``pure long-range molecule'' states (Re=28R_{e} = 28Re​=28 and 39 {\\AA} in 39K2^{39}K_{2}39K2​) as well as long-range levels of known short range states with outer classical turning points of sim20−250AA\\sim 20 - 250 {\\AA}sim20−250AA. Such spectra have been observed by ``trap loss'' (decrease in atomic fluorescence), molecular ionization, and fragment ionization. Optical-optical double resonance (OODR), e.g. through the ``Franck-Condon windows'' of the ``pure long-range'' states, produces readily assignable spectra at higher asymptotes as well. Further extensions of ultracold photoassociative spectroscopy and applications to determination of long range potentials, atomic properties, and Bose-Einstein condensate stability will be presented.
Diatomic potentials for krypton are computed and also probed experimentally. For a probe-laser wavelength near 811811811 nm, several strong dipole-dipole interactions produce purely-long-range potential wells in the singly excited manifold of (s+ps+ps+p) potentials and in the doubly excited manifold of (p+pp+pp+p) and (s+ds+ds+d) potentials. Evidence of resonant photoassociation into bound states of these potential wells is observed in the emission of ions and ultraviolet photons from a magneto-optically trapped krypton cloud.
A new laser spectroscopic technique has been demonstrated for examining the structure of alkali--rare gas diatomic electronic states near the classical limit. In two-color experiments, Rb--Ar or Rb--Kr thermal pairs are excited by freeleftarrowleftarrowleftarrowfree or boundleftarrowleftarrowleftarrowfree transitions while monitoring the amplified spontaneous emission produced on the Rb D1_11​ or D2_22​ lines. Spectra observed lying within 10 cm−1^{-1}−1 of the separated atom limit for the A2Pi1/2^{2}Pi_{1/2}2Pi1/2​ states of Rb--Ar and Rb--Kr will be presented and discussed.