Physical Review A

Measurement of product rotational alignment in associative-ionization collisions between polarized Na(3p) atoms

M-X. Wang, Mattanjah S. de Vries, J. Weiner

Published Jan 1, 1986• 13 citations

Abstract

We have studied the effect of reactant Na(3p) polarization on the rotational angular momentum alignment of product ${\mathrm{Na}}_{2}$${\mathrm{}}^{+}$ ions arising from associative-ionization (AI) collisions. Our results show that sensitivity of the AI rate constant to initial atomic polarization persists even when all hyperfine states are populated with broadband (3 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) pulsed laser excitation of Na${(\mathrm{}}^{2}$${P}_{3/2}$) and that the spatial distribution of product rotational angular momentum vectors is anisotropic. We discuss a qualitative description of the collision process consistent with our measurements which indicates that \ensuremath{\sigma}-orbital symmetry is preferred to \ensuremath{\pi}-orbital symmetry as the colliding partners approach.

DOI: 10.1103/physreva.33.765

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Theory of the polarization dependence of reactive collisions and its application to the associative ionization process 2Na(3 P3/22 )→ Na2 + (X 2 Σg+ )+ e−

Dumont M. Jones, John S. Dahler

Physical Review AMay 1, 198716 citations

Mechanism of collisionally induced transitions among fine-structure levels: Semiclassical calculations of alignment effects in the Na–He system

Laurie J. Kovalenko, Stephen R. Leone, J. B. Delos

The Journal of Chemical PhysicsDec 1, 198947 citations

Polarization Dependence of Associative Ionization of Laser-Excited Na(3p)P322 Atoms

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Physical Review LettersMar 1, 198274 citations

Ultracold photoassociative ionization collisions in an atomic beam: Optical field intensity and polarization dependence of the rate constant

Chun-Cheng Tsao, Reginaldo de Jesus Napolitano, Yang Wang +1 more

Physical Review AJan 1, 199511 citations

Anisotropy quantum beat in two-photon ionization of coherently excited hyperfine states of Na

Young Jong Lee, Sung Haeng Cho, Nam Joon Kim +1 more

The Journal of Chemical PhysicsJul 8, 20013 citations

Velocity-selected atomic-beam collisions in the energy range from 300 to 5 K

Yinde Wang, J. Weiner

Physical Review AJul 1, 199013 citations

Physical Review A

Measurement of product rotational alignment in associative-ionization collisions between polarized Na(3p) atoms

M-X. Wang, Mattanjah S. de Vries, J. Weiner

Published Jan 1, 1986• 13 citations

Publisher

Abstract

We have studied the effect of reactant Na(3p) polarization on the rotational angular momentum alignment of product

{\mathrm{Na}}_{2}$${\mathrm{}}^{+}

ions arising from associative-ionization (AI) collisions. Our results show that sensitivity of the AI rate constant to initial atomic polarization persists even when all hyperfine states are populated with broadband (3

{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}

) pulsed laser excitation of Na

{(\mathrm{}}^{2}$${P}_{3/2}

) and that the spatial distribution of product rotational angular momentum vectors is anisotropic. We discuss a qualitative description of the collision process consistent with our measurements which indicates that \ensuremath{\sigma}-orbital symmetry is preferred to \ensuremath{\pi}-orbital symmetry as the colliding partners approach.

DOI: 10.1103/physreva.33.765

Related papers

Theory of the polarization dependence of reactive collisions and its application to the associative ionization process 2Na(3 P3/22 )→ Na2 + (X 2 Σg+ )+ e−

Dumont M. Jones, John S. Dahler

We consider collisions between (quasi-) one- or two-electron atoms, each of which has been prepared in a fixed distribution of hyperfine magnetic substates. The resulting ``polarization-dependent'' reaction rates are functions of (1) the (experimentally adjustable) orientation of the quantization axis associated with the hyperfine substates, (2) the hyperfine terms of the colliding atoms, and (3) the detailed reaction dynamics as characterized by preparation- and fine-structure-independent cross sections. These effects are deconvoluted and analyzed, and their use in elucidating reaction mechanisms is discussed. Particular emphasis is placed on the associative ionization of two Na(3p) atoms, each prepared by adsorption of resonant laser photons. The quasimolecular states of Na...Na that might react in this case are limited by selection rules. More information on the reaction mechanism is then obtained by using experimental data, in combination with the formal analysis, to draw further conclusions about the active quasimolecular states.We consider collisions between (quasi-) one- or two-electron atoms, each of which has been prepared in a fixed distribution of hyperfine magnetic substates. The resulting ``polarization-dependent'' reaction rates are functions of (1) the (experimentally adjustable) orientation of the quantization axis associated with the hyperfine substates, (2) the hyperfine terms of the colliding atoms, and (3) the detailed reaction dynamics as characterized by preparation- and fine-structure-independent cross sections. These effects are deconvoluted and analyzed, and their use in elucidating reaction mechanisms is discussed. Particular emphasis is placed on the associative ionization of two Na(3p) atoms, each prepared by adsorption of resonant laser photons. The quasimolecular states of Na...Na that might react in this case are limited by selection rules. More information on the reaction mechanism is then obtained by using experimental data, in combination with the formal analysis, to draw further conclusions about the active quasimolecular states.

Physical Review AMay 1, 198716 citations

Mechanism of collisionally induced transitions among fine-structure levels: Semiclassical calculations of alignment effects in the Na–He system

Laurie J. Kovalenko, Stephen R. Leone, J. B. Delos

To gain insight into the mechanism of Na(3p)2P3/2→2P1/2 fine-structure transitions induced by collision with He, we monitor the expectation values of the orbital- and spin-angular momentum vectors, l and s, as a function of time along the trajectory, using a semiclassical formalism. In a typical collision, 〈s〉 remains nearly space-fixed while 〈l〉 precesses about the rotating internuclear axis. Thus, in the interaction region, the projection of 〈l〉 onto the internuclear axis, 〈λ〉, remains nearly constant, and the molecular alignment of the orbital is preserved. We show how equations of motion for the classical analogues of these expectation values agree qualitatively with the quantum equations of motion. A qualitative comparison is also made with the Cs–He system for which the spin–orbit coupling is much stronger. We calculate cross sections for Na(2P3/2)+He→Na(2P1/2)+He as a function of the alignment of the excitation laser polarization with respect to the asymptotic relative velocity vector. For stationary pumping of the excited F=3 hyperfine level, this calculation predicts that the perpendicular alignment gives a cross section which is larger by a factor of 1.8 than that obtained by parallel alignment.To gain insight into the mechanism of Na(3p)2P3/2→2P1/2 fine-structure transitions induced by collision with He, we monitor the expectation values of the orbital- and spin-angular momentum vectors, l and s, as a function of time along the trajectory, using a semiclassical formalism. In a typical collision, 〈s〉 remains nearly space-fixed while 〈l〉 precesses about the rotating internuclear axis. Thus, in the interaction region, the projection of 〈l〉 onto the internuclear axis, 〈λ〉, remains nearly constant, and the molecular alignment of the orbital is preserved. We show how equations of motion for the classical analogues of these expectation values agree qualitatively with the quantum equations of motion. A qualitative comparison is also made with the Cs–He system for which the spin–orbit coupling is much stronger. We calculate cross sections for Na(2P3/2)+He→Na(2P1/2)+He as a function of the alignment of the excitation laser polarization with respect to the asymptotic relative velocity vector. For stationary pumping of the excited F=3 hyperfine level, this calculation predicts that the perpendicular alignment gives a cross section which is larger by a factor of 1.8 than that obtained by parallel alignment.

The Journal of Chemical PhysicsDec 1, 198947 citations

Polarization Dependence of Associative Ionization of Laser-Excited Na(3p)P322 Atoms

Joost Kircz, Reinhard Morgenstern, Gerard Nienhuis

The associative ionization ${\mathrm{Na}}^{*}+{\mathrm{Na}}^{*}\ensuremath{\rightarrow}{{\mathrm{Na}}_{2}}^{+}+e$, when Na atoms in a single thermal beam are excited by linearly polarized light, was observed. The ion yield increases by a factor of 1.7 when the light polarization vector is rotated from a perpendicular to a parallel direction with respect to the beam. A theoretical analysis shows that the ionization rates $K$ obey the relations $K(\frac{1}{2}, \frac{3}{2})=0$ and $K(\frac{1}{2}, \frac{1}{2})=1.4K(\frac{3}{2}, \frac{3}{2})$ , where the arguments indicate the initial magnetic substates $|{M}_{J}|$ of the two colliding atoms.The associative ionization ${\mathrm{Na}}^{*}+{\mathrm{Na}}^{*}\ensuremath{\rightarrow}{{\mathrm{Na}}_{2}}^{+}+e$, when Na atoms in a single thermal beam are excited by linearly polarized light, was observed. The ion yield increases by a factor of 1.7 when the light polarization vector is rotated from a perpendicular to a parallel direction with respect to the beam. A theoretical analysis shows that the ionization rates $K$ obey the relations $K(\frac{1}{2}, \frac{3}{2})=0$ and $K(\frac{1}{2}, \frac{1}{2})=1.4K(\frac{3}{2}, \frac{3}{2})$, where the arguments indicate the initial magnetic substates $|{M}_{J}|$ of the two colliding atoms.

Physical Review LettersMar 1, 198274 citations

Ultracold photoassociative ionization collisions in an atomic beam: Optical field intensity and polarization dependence of the rate constant

Chun-Cheng Tsao, Reginaldo de Jesus Napolitano, Yang Wang +1 more

We report here measurements of two-body photoassociative ionization collisions between sodium atoms within an ultranarrow velocity class selected from a well-collimated, thermal atomic beam. Doppler-shifted excitation of the Na(3s ${\mathrm{}}^{2}$ ${\mathit{S}}_{1/2}$ ;F=1)\ensuremath{\rightarrow}Na(5p ${\mathrm{}}^{2}$ ${\mathit{P}}_{3/2}$ ) transition at 285 nm by a single-mode laser defines the narrow velocity class that subsequently populates the F=2 hyperfine level of the Na ground state by optical pumping. Probe laser beam excitation tuned near the Na(3s ${\mathrm{}}^{2}$ ${\mathit{S}}_{1/2}$ ;F=2)\ensuremath{\rightarrow}Na(3p ${\mathrm{}}^{2}$ ${\mathit{P}}_{3/2}$ ;F=3) transition produced photoassociative ionization with an average collision energy ${\mathit{E}}_{\mathit{K}}$ corresponding to a temperature of 5.3 mK ( ${\mathit{E}}_{\mathit{K}}$ =3/2kT). We determine the rate constant for the process as a function of probe beam intensity and polarization.We report here measurements of two-body photoassociative ionization collisions between sodium atoms within an ultranarrow velocity class selected from a well-collimated, thermal atomic beam. Doppler-shifted excitation of the Na(3s${\mathrm{}}^{2}$${\mathit{S}}_{1/2}$;F=1)\ensuremath{\rightarrow}Na(5p${\mathrm{}}^{2}$${\mathit{P}}_{3/2}$) transition at 285 nm by a single-mode laser defines the narrow velocity class that subsequently populates the F=2 hyperfine level of the Na ground state by optical pumping. Probe laser beam excitation tuned near the Na(3s${\mathrm{}}^{2}$${\mathit{S}}_{1/2}$;F=2)\ensuremath{\rightarrow}Na(3p${\mathrm{}}^{2}$${\mathit{P}}_{3/2}$;F=3) transition produced photoassociative ionization with an average collision energy ${\mathit{E}}_{\mathit{K}}$ corresponding to a temperature of 5.3 mK (${\mathit{E}}_{\mathit{K}}$=3/2kT). We determine the rate constant for the process as a function of probe beam intensity and polarization.

Physical Review AJan 1, 199511 citations

Anisotropy quantum beat in two-photon ionization of coherently excited hyperfine states of Na

Young Jong Lee, Sung Haeng Cho, Nam Joon Kim +1 more

A new method is proposed that utilizes the quantum beat of polarization anisotropy in two-photon ionization of atoms and molecules. It was shown that the frequency and the amplitude of the beating anisotropy contain information on, respectively, the hyperfine constants of the electronically excited state and the branching ratio of the photoionization channels leading to different photoelectron angular momentum states in the ionization continuum. The method was demonstrated for the case of the Na 3p P3/22 state by the time-resolved two-photon ionization with two pulses of parallel and perpendicular polarizations.A new method is proposed that utilizes the quantum beat of polarization anisotropy in two-photon ionization of atoms and molecules. It was shown that the frequency and the amplitude of the beating anisotropy contain information on, respectively, the hyperfine constants of the electronically excited state and the branching ratio of the photoionization channels leading to different photoelectron angular momentum states in the ionization continuum. The method was demonstrated for the case of the Na 3p P3/22 state by the time-resolved two-photon ionization with two pulses of parallel and perpendicular polarizations.

The Journal of Chemical PhysicsJul 8, 20013 citations

Velocity-selected atomic-beam collisions in the energy range from 300 to 5 K

Yinde Wang, J. Weiner

We report cross-section measurements of the associative-ionization process, Na(3 ${\mathit{p}}^{2}$ ${\mathit{P}}_{3/2}$ )+Na(3 ${\mathit{p}}^{2}$ ${\mathit{P}}_{3/2}$ )\ensuremath{\rightarrow} ${\mathrm{Na}}_{2}^{+}$ +e as a function of velocity, alignment, and orientation in the collision energy range from 300 to 5 K. Two independently tunable laser beams select narrow velocity classes of excited sodium in a well-collimated atomic beam. Circular and linear polarization of the excitation lasers permits alignment and orientation of the excited atoms in the two velocity classes. The excitation functions show pronounced differences reflecting different molecular pathways to the final product, and they bridge the energy range between conventional and ``cold'' collision dynamics.We report cross-section measurements of the associative-ionization process, Na(3${\mathit{p}}^{2}$${\mathit{P}}_{3/2}$)+Na(3${\mathit{p}}^{2}$${\mathit{P}}_{3/2}$)\ensuremath{\rightarrow}${\mathrm{Na}}_{2}^{+}$+e as a function of velocity, alignment, and orientation in the collision energy range from 300 to 5 K. Two independently tunable laser beams select narrow velocity classes of excited sodium in a well-collimated atomic beam. Circular and linear polarization of the excitation lasers permits alignment and orientation of the excited atoms in the two velocity classes. The excitation functions show pronounced differences reflecting different molecular pathways to the final product, and they bridge the energy range between conventional and ``cold'' collision dynamics.

Physical Review AJul 1, 199013 citations

We have studied the effect of reactant Na(3p) polarization on the rotational angular momentum alignment of product

{\mathrm{Na}}_{2}$${\mathrm{}}^{+}

{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}

) pulsed laser excitation of Na

{(\mathrm{}}^{2}$${P}_{3/2}

K

obey the relations

K(\frac{1}{2}, \frac{3}{2})=0

and

K(\frac{1}{2}, \frac{1}{2})=1.4K(\frac{3}{2}, \frac{3}{2})

, where the arguments indicate the initial magnetic substates

|{M}_{J}|

of the two colliding atoms.

{\mathrm{}}^{2}

{\mathit{S}}_{1/2}

;F=1)\ensuremath{\rightarrow}Na(5p

{\mathrm{}}^{2}

{\mathit{P}}_{3/2}

) transition at 285 nm by a single-mode laser defines the narrow velocity class that subsequently populates the F=2 hyperfine level of the Na ground state by optical pumping. Probe laser beam excitation tuned near the Na(3s

{\mathrm{}}^{2}

{\mathit{S}}_{1/2}

;F=2)\ensuremath{\rightarrow}Na(3p

{\mathrm{}}^{2}

{\mathit{P}}_{3/2}

;F=3) transition produced photoassociative ionization with an average collision energy

{\mathit{E}}_{\mathit{K}}

corresponding to a temperature of 5.3 mK (

{\mathit{E}}_{\mathit{K}}

=3/2kT). We determine the rate constant for the process as a function of probe beam intensity and polarization.

We report cross-section measurements of the associative-ionization process, Na(3

{\mathit{p}}^{2}

{\mathit{P}}_{3/2}

)+Na(3

{\mathit{p}}^{2}

{\mathit{P}}_{3/2}

)\ensuremath{\rightarrow}

{\mathrm{Na}}_{2}^{+}

+e as a function of velocity, alignment, and orientation in the collision energy range from 300 to 5 K. Two independently tunable laser beams select narrow velocity classes of excited sodium in a well-collimated atomic beam. Circular and linear polarization of the excitation lasers permits alignment and orientation of the excited atoms in the two velocity classes. The excitation functions show pronounced differences reflecting different molecular pathways to the final product, and they bridge the energy range between conventional and ``cold'' collision dynamics.