Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

The Journal of Chemical Physics

Alignment of Hg–Ar van der Waals molecule photofragments following photodissociation

C. J. K. Quayle, I. M. Bell, Endre Takács, X. Chen, Keith R. Burnett, D. M. Segal

Published Dec 15, 1993• 19 citations
Publisher

Abstract

We have measured the alignment of the photofragments produced by photodissociation of Hg–Ar van der Waals molecules using light around 253.7 nm. The molecules are produced in the X0+ ground state in a supersonic expansion. Tunable laser light close to the Hg 6 1S0–6 3P1 transition is then used to excite the molecule to the B1± state, in which it dissociates. The alignment of the resulting Hg(3P1) asymptotic atoms is probed by tuning a delayed second laser to the 435.8 nm Hg 6 3P1–7 3S1 atomic transition and monitoring the subsequent fluorescence on the 7 3S1–6 3P2 transition around 546.1 nm. These measurements have been made, we believe for the first time, as a function of dissociating energy from very close to threshold to higher energies. The alignment shows a significant rise with increasing photon energy in line with a semiclassical picture of orbital locking at lower energies and rapid decoupling at higher energies. The results exhibit good agreement with the results of a fully quantum mechanical theory of the system.

DOI
10.1063/1.465494

Related papers

Collisional redistribution in Hg-Kr: Polarization spectrum of the redistributed light

I. M. Bell, C. J. K. Quayle, Keith R. Burnett +1 more

We have measured the alignment of Hg(6 $^{3}$${\mathit{P}}_{1}$) atoms following off-resonant excitation of the Hg 6 $^{1}\mathrm{S}_{0}$--6 $^{3}\mathrm{P}_{1}$ transition in the presence of Kr. We present a polarization spectrum for both red and blue wings out to detunings beyond 100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. This represents a considerable extension to the existing results, which has been made possible by the use of a pump-and-probe excitation scheme. In the experiment a pulsed laser, detuned from the resonance, creates an alignment in the upper state. This is probed by tuning a delayed second laser to a higher transition and monitoring laser-induced fluorescence from the two-step process. The alignment of the asymptotic Hg(6 $^{3}$${\mathit{P}}_{1}$) atoms is determined by comparison of the signals obtained for different relative polarizations of the lasers. We discuss the advantages of this method and the relation of the raw data to the polarizations presented. The results are discussed within the context of a simple quasiclassical model of the process.

Physical Review A•Apr 1, 1993•8 citations

Hyperfine structure effects in probing atomic alignment

I. M. Bell, C. J. K. Quayle, Keith R. Burnett

We have performed an analysis of the effect of hyperfine structure in an experiment in which an aligned excited state is probed using linearly polarized light. The state is born with a given electronic alignment resulting from a collisional process. It is probed after a time which is short in comparison to its radiative lifetime but much longer than ω−1hfs, where ℏωhfs is the hyperfine splitting. This means that hyperfine structure has ample time to ‘‘develop.’’ It is therefore essential to take into account both the hyperfine structure of the level and the manner in which the alignment is affected by recoupling to the new basis. Ratios of fluorescent intensities for different laser polarization configurations contain information on the alignment of the system. We show how these may be calculated for a system with several isotopes, some of which have hyperfine structure, and where many components are probed with appreciable strength. A comparison is made with our experimental results for the Hg(6 3P1) level probed on the 6 3P1–7 3S1 transition. The presence of hyperfine structure has a considerable influence on the measurements. It is important to understand such effects if one is to obtain information on the nascent electronic alignment by observation of the fluorescent intensities.

The Journal of Chemical Physics•Feb 1, 1995•1 citation

HgIn photoassociation, bound-bound transitions, and excimer emission

Paola Bicchi, C. Marinelli, Robert A. Bernheim

Laser excitation of In atoms at the $6{}^{2}{S}_{1/2}--5{}^{2}{P}_{1/2}$ atomic resonance transition wavelength of 410.3 nm in the presence of Hg vapor produces several types of emission features: HgIn excimer satellites on the red wings of the In resonance fluorescence transitions at 410.3 and 451.1 nm, bound-bound HgIn molecular fluorescence at 499 and 522 nm resulting from photoassociation of $\mathrm{In}(6{}^{2}{S}_{1/2})$ with $\mathrm{Hg}(6{}^{1}{S}_{0}),$ and UV atomic fluorescence from the $\mathrm{In}(5{}^{2}D)$ states that lie at energies above the $\mathrm{In}(6{}^{2}{S}_{1/2}--5{}^{2}{P}_{1/2})$ excitation. These various spectral features are interpreted in terms of a proposed HgIn potential-energy level diagram with additional information from measured excited-state lifetimes and the power dependence of the laser excitation at 410.3 and 522 nm. Direct excitation of the 499 and 522 nm HgIn bound-bound transitions also produces emission at 410.3 and 451.1 nm resulting from collisional dissociation of the excited HgIn states.

Physical Review A•Sep 1, 1997•6 citations

Transition from second- to first-order dipole-dipole interaction in the excited EuSr molecule

Kay Niemax

For the first time a transition from a second- to first-order dipole-dipole interaction (van der Waals to resonance interaction) has been observed in a study of the excited EuSr molecule which dissociates into europium 4${\mathrm{f}}^{7}$5s6p ${\mathrm{}}^{8}$${\mathrm{P}}_{9/2}$ and strontium 5${\mathrm{s}}^{2}$ ${\mathrm{}}^{1}$${\mathrm{P}}_{1}$ atoms. The transition was verified by measurement of the wavelength dependence in the quasistatic wings of the cw-laser--excited 4595.3-A\r{} line in Eu broadened by Sr ground-state atoms.

Physical Review Letters•Jul 1, 1985•19 citations

Interference in atomic fluorescence excited by molecular photodissociation

Gerald J. Diebold

In photodissociation of a homonuclear diatomic molecule, conservation of linear and angular momenta requires that each atomic fragment follow identical but oppositely directed trajectories with respect to the molecular center of mass. For certain values of the incident photon energy, one of the atoms will be electronically excited while the other will be in its ground state. When a detector records the undispersed fluorescence from the decay of the excited atom it cannot distinguish which trajectory the excited atom followed and hence whether the photon possesses a blue or red Doppler shift corresponding to recoil towards or away from the detector. According to the principle of superposition in quantum mechanics, the wave function of the photon must be a sum over two paths corresponding to emission from an excited atom in either of the two recoil directions. Detection of such photons gives rise to an interference between the probability amplitudes for the two paths that is manifested in the output from the photodetector as a beat frequency. Since photodissociation of an ensemble of molecules gives rise to a distribution of recoil directions relative to the electric vector of the incident radiation, a range of beat frequencies must be present in the detected signal. This paper gives a calculation of expected output voltage waveforms from a photodetector viewing atomic fluorescence excited by molecular photodissociation. Expressions are given for partial Fourier transforms of the photodetector signals. The results show that the shape of the voltage waveforms depends strongly on the asymmetry parameter for recoil of the photofragments and on whether or not the magnetic sublevels of the excited atomic state are created in a coherent superposition.

Physical Review A•Sep 1, 1985•4 citations

Coherence effects in half collisions: Collision induced fluorescence in Hg(2537 Å)–Ar

D. Segal, I. D. Harris

We have measured the polarization of collisionally redistributed light as a function of detuning from line center for the Hg3P1–1S0 transition in the presence of Ar. We present a polarization profile for the red wing between 5 and 18 cm−1 and polarizations for two detunings in the blue wing. We compare this type of experiment to the complementary method of photodissociation and discuss the issue of coherence between excitation path-ways. The data are analyzed using a simple molecular reorientation model suggested by others which includes coherent excitation. The model is shown to be unable to completely account for the high polarizations measured in this experiment. We suggest reasons for the failure of this model.

The Journal of Chemical Physics•Feb 15, 1991•10 citations
We have measured the alignment of the photofragments produced by photodissociation of Hg–Ar van der Waals molecules using light around 253.7 nm. The molecules are produced in the X0+ ground state in a supersonic expansion. Tunable laser light close to the Hg 6 1S0–6 3P1 transition is then used to excite the molecule to the B1± state, in which it dissociates. The alignment of the resulting Hg(3P1) asymptotic atoms is probed by tuning a delayed second laser to the 435.8 nm Hg 6 3P1–7 3S1 atomic transition and monitoring the subsequent fluorescence on the 7 3S1–6 3P2 transition around 546.1 nm. These measurements have been made, we believe for the first time, as a function of dissociating energy from very close to threshold to higher energies. The alignment shows a significant rise with increasing photon energy in line with a semiclassical picture of orbital locking at lower energies and rapid decoupling at higher energies. The results exhibit good agreement with the results of a fully quantum mechanical theory of the system.
We have measured the alignment of Hg(6 3^{3}3P1{\mathit{P}}_{1}P1​) atoms following off-resonant excitation of the Hg 6 1S0^{1}\mathrm{S}_{0}1S0​--6 3P1^{3}\mathrm{P}_{1}3P1​ transition in the presence of Kr. We present a polarization spectrum for both red and blue wings out to detunings beyond 100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. This represents a considerable extension to the existing results, which has been made possible by the use of a pump-and-probe excitation scheme. In the experiment a pulsed laser, detuned from the resonance, creates an alignment in the upper state. This is probed by tuning a delayed second laser to a higher transition and monitoring laser-induced fluorescence from the two-step process. The alignment of the asymptotic Hg(6 3^{3}3P1{\mathit{P}}_{1}P1​) atoms is determined by comparison of the signals obtained for different relative polarizations of the lasers. We discuss the advantages of this method and the relation of the raw data to the polarizations presented. The results are discussed within the context of a simple quasiclassical model of the process.
We have performed an analysis of the effect of hyperfine structure in an experiment in which an aligned excited state is probed using linearly polarized light. The state is born with a given electronic alignment resulting from a collisional process. It is probed after a time which is short in comparison to its radiative lifetime but much longer than ω−1hfs, where ℏωhfs is the hyperfine splitting. This means that hyperfine structure has ample time to ‘‘develop.’’ It is therefore essential to take into account both the hyperfine structure of the level and the manner in which the alignment is affected by recoupling to the new basis. Ratios of fluorescent intensities for different laser polarization configurations contain information on the alignment of the system. We show how these may be calculated for a system with several isotopes, some of which have hyperfine structure, and where many components are probed with appreciable strength. A comparison is made with our experimental results for the Hg(6 3P1) level probed on the 6 3P1–7 3S1 transition. The presence of hyperfine structure has a considerable influence on the measurements. It is important to understand such effects if one is to obtain information on the nascent electronic alignment by observation of the fluorescent intensities.
Laser excitation of In atoms at the 62S1/2−−52P1/26{}^{2}{S}_{1/2}--5{}^{2}{P}_{1/2}62S1/2​−−52P1/2​ atomic resonance transition wavelength of 410.3 nm in the presence of Hg vapor produces several types of emission features: HgIn excimer satellites on the red wings of the In resonance fluorescence transitions at 410.3 and 451.1 nm, bound-bound HgIn molecular fluorescence at 499 and 522 nm resulting from photoassociation of In(62S1/2)\mathrm{In}(6{}^{2}{S}_{1/2})In(62S1/2​) with Hg(61S0),\mathrm{Hg}(6{}^{1}{S}_{0}),Hg(61S0​), and UV atomic fluorescence from the In(52D)\mathrm{In}(5{}^{2}D)In(52D) states that lie at energies above the In(62S1/2−−52P1/2)\mathrm{In}(6{}^{2}{S}_{1/2}--5{}^{2}{P}_{1/2})In(62S1/2​−−52P1/2​) excitation. These various spectral features are interpreted in terms of a proposed HgIn potential-energy level diagram with additional information from measured excited-state lifetimes and the power dependence of the laser excitation at 410.3 and 522 nm. Direct excitation of the 499 and 522 nm HgIn bound-bound transitions also produces emission at 410.3 and 451.1 nm resulting from collisional dissociation of the excited HgIn states.
For the first time a transition from a second- to first-order dipole-dipole interaction (van der Waals to resonance interaction) has been observed in a study of the excited EuSr molecule which dissociates into europium 4${\mathrm{f}}^{7}$5s6p 8{\mathrm{}}^{8}8P9/2{\mathrm{P}}_{9/2}P9/2​ and strontium 5s2{\mathrm{s}}^{2}s2 1{\mathrm{}}^{1}1P1{\mathrm{P}}_{1}P1​ atoms. The transition was verified by measurement of the wavelength dependence in the quasistatic wings of the cw-laser--excited 4595.3-A\r{} line in Eu broadened by Sr ground-state atoms.
In photodissociation of a homonuclear diatomic molecule, conservation of linear and angular momenta requires that each atomic fragment follow identical but oppositely directed trajectories with respect to the molecular center of mass. For certain values of the incident photon energy, one of the atoms will be electronically excited while the other will be in its ground state. When a detector records the undispersed fluorescence from the decay of the excited atom it cannot distinguish which trajectory the excited atom followed and hence whether the photon possesses a blue or red Doppler shift corresponding to recoil towards or away from the detector. According to the principle of superposition in quantum mechanics, the wave function of the photon must be a sum over two paths corresponding to emission from an excited atom in either of the two recoil directions. Detection of such photons gives rise to an interference between the probability amplitudes for the two paths that is manifested in the output from the photodetector as a beat frequency. Since photodissociation of an ensemble of molecules gives rise to a distribution of recoil directions relative to the electric vector of the incident radiation, a range of beat frequencies must be present in the detected signal. This paper gives a calculation of expected output voltage waveforms from a photodetector viewing atomic fluorescence excited by molecular photodissociation. Expressions are given for partial Fourier transforms of the photodetector signals. The results show that the shape of the voltage waveforms depends strongly on the asymmetry parameter for recoil of the photofragments and on whether or not the magnetic sublevels of the excited atomic state are created in a coherent superposition.
We have measured the polarization of collisionally redistributed light as a function of detuning from line center for the Hg3P1–1S0 transition in the presence of Ar. We present a polarization profile for the red wing between 5 and 18 cm−1 and polarizations for two detunings in the blue wing. We compare this type of experiment to the complementary method of photodissociation and discuss the issue of coherence between excitation path-ways. The data are analyzed using a simple molecular reorientation model suggested by others which includes coherent excitation. The model is shown to be unable to completely account for the high polarizations measured in this experiment. We suggest reasons for the failure of this model.