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Quantum Controlled Cold Scattering Between Simple Atoms and Diatoms.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Quantum Controlled Cold Scattering Between Simple Atoms and Diatoms./
作者:	Zhou, Haowen.
面頁冊數:	1 online resource (153 pages)
附註:	Source: Dissertations Abstracts International, Volume: 84-10, Section: B.
Contained By:	Dissertations Abstracts International84-10B.
標題:	Cold. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30363160click for full text (PQDT)
ISBN:	9798377681755

Quantum Controlled Cold Scattering Between Simple Atoms and Diatoms.
Zhou, Haowen.

Quantum Controlled Cold Scattering Between Simple Atoms and Diatoms. - 1 online resource (153 pages)

Source: Dissertations Abstracts International, Volume: 84-10, Section: B.

Thesis (Ph.D.)--Stanford University, 2023.

Includes bibliographical references

This thesis presents the experimental studies of quantum-controlled cold scattering of H2 isotopologues (HD, D2) with simple rare gas atoms (He, Ne) and diatom molecules D2. In these experiments, we prepare HD and D2 molecules in specific rovibrational levels (v = 2, 4, j = 2, 4) with defined alignments, and study their rotational inelastic scatterings of the state-prepared molecules at low collision temperatures. From a time-of-flight apparatus, we extract information about the angular distributions of the scattered products, therefore providing insights into the dynamics of the collision processes. By combining quantum-state control and low-energy scattering, we are able to interrogate the fundamental interactions between such simple atoms and diatoms at an unprecedented level of detail.Many experimental techniques have enabled us to achieve this goal. In particular, our unique ability lies in the state preparation of rovibrationally excited H2 and isotopolgues, which is achieved by a coherent optical technique called Stark-induced adiabatic Raman passage (SARP). SARP combines two nanosecond high-power laser pulses with specific temporal delay and intensity ratio, and is able to transfer the near complete ground state population into the desired (v, j) state. The state-specific detection of the scattered products is then done by resonance enhanced multiphoton ionization (REMPI). For the cold scattering temperature (~1 K), it is realized using supersonic coexpansion of a gas mixture into a single molecular beam. This technique exploits the velocity spread inside a molecular beam, which results in low relative collision speeds but a somewhat broad distribution.Understanding molecular interactions is a collective effort of both experiment and theory. Typically, cross sections are measured as a function of the scattering temperature, and peaks are identified which indicate the presence of scattering resonances. These resonances correspond to the quasi-bound states formed within the energy well of the interaction potential which is raised by centrifugal barriers of various orbital angular momentum l. As such, they become the most sensitive probe of the intermolecular forces between the two colliding species, especially the long-range part at low scattering energies. Theoretically, computation programs have been built to predict locations and intensities of the scattering resonances from a given potential. These calculations are benefited from experimental measurements in terms of refining the semiempirical parameters, or the ab initio methods used to generate the potential energies.In our experimental approach, because of the broad collision temperature distribution present, we adopted a different approach which looks into the stereodynamics and the differential cross section of a scattering process. In the presence of a single resonance, the angular distribution of the scattered products demonstrates characteristic features, and we can thus identify scattering resonances through partial wave fittings of the measured distribution. As an example, we have determined an l = 2 resonance of the D2-He Δj = 2 relaxation by measuring the stereodynamics at different collision geometries. More studies seem to indicate this as a robust feature, even if we change the collision partner or change the rovibrational excitations. However, this is in contrast with the previous theoretical predictions of a more predominant l = 1 resonance within our collision temperature range. We later indeed found a l = 1 resonance in the HD-He Δj = 1 interaction, but the agreement shows up only in this case. The continuing discrepancy may point to some subtle differences in the anisotropic part of the H2-He interaction potential, but more works should be made to reach a conclusion.The study does not limit here. With the help of SARP state preparation, we are able to perform a series of experiments which investigate the effects of different vibrational excitations, different rotational excitations, as well as different collision partners. For the Δj = 2 rotationally inelastic scattering, we have studied collisions of D2 or HD, with He or Ne, and from (v = 2) or (v = 4) state. While the total cross sections may vary, we found mostly very similar l = 2 resonance characters and similar stereodynamics. For scatterings from (j = 4) to (j' = 2), however, several possible m'-states of the scattered products need to be included, leading to different angular distributions. SARP also manipulates the molecular alignments which prepares them in different incoming m-state superpositions. In particular, we prepare an exotic biaxial state where the diatom bond axis aligns simultaneously in two directions. By decomposing each axis direction separately and preparing the two corresponding uniaxial states, we are able to demonstrate an interference effect in low-energy scattering from the biaxial state. It is in analogue with a double slit where the two axis directions act as the two slits.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798377681755Subjects--Topical Terms:

560283
Cold.
Index Terms--Genre/Form:

542853
Electronic books.

Quantum Controlled Cold Scattering Between Simple Atoms and Diatoms.
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500 $a Source: Dissertations Abstracts International, Volume: 84-10, Section: B.
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502 $a Thesis (Ph.D.)--Stanford University, 2023.
504 $a Includes bibliographical references
520 $a This thesis presents the experimental studies of quantum-controlled cold scattering of H2 isotopologues (HD, D2) with simple rare gas atoms (He, Ne) and diatom molecules D2. In these experiments, we prepare HD and D2 molecules in specific rovibrational levels (v = 2, 4, j = 2, 4) with defined alignments, and study their rotational inelastic scatterings of the state-prepared molecules at low collision temperatures. From a time-of-flight apparatus, we extract information about the angular distributions of the scattered products, therefore providing insights into the dynamics of the collision processes. By combining quantum-state control and low-energy scattering, we are able to interrogate the fundamental interactions between such simple atoms and diatoms at an unprecedented level of detail.Many experimental techniques have enabled us to achieve this goal. In particular, our unique ability lies in the state preparation of rovibrationally excited H2 and isotopolgues, which is achieved by a coherent optical technique called Stark-induced adiabatic Raman passage (SARP). SARP combines two nanosecond high-power laser pulses with specific temporal delay and intensity ratio, and is able to transfer the near complete ground state population into the desired (v, j) state. The state-specific detection of the scattered products is then done by resonance enhanced multiphoton ionization (REMPI). For the cold scattering temperature (~1 K), it is realized using supersonic coexpansion of a gas mixture into a single molecular beam. This technique exploits the velocity spread inside a molecular beam, which results in low relative collision speeds but a somewhat broad distribution.Understanding molecular interactions is a collective effort of both experiment and theory. Typically, cross sections are measured as a function of the scattering temperature, and peaks are identified which indicate the presence of scattering resonances. These resonances correspond to the quasi-bound states formed within the energy well of the interaction potential which is raised by centrifugal barriers of various orbital angular momentum l. As such, they become the most sensitive probe of the intermolecular forces between the two colliding species, especially the long-range part at low scattering energies. Theoretically, computation programs have been built to predict locations and intensities of the scattering resonances from a given potential. These calculations are benefited from experimental measurements in terms of refining the semiempirical parameters, or the ab initio methods used to generate the potential energies.In our experimental approach, because of the broad collision temperature distribution present, we adopted a different approach which looks into the stereodynamics and the differential cross section of a scattering process. In the presence of a single resonance, the angular distribution of the scattered products demonstrates characteristic features, and we can thus identify scattering resonances through partial wave fittings of the measured distribution. As an example, we have determined an l = 2 resonance of the D2-He Δj = 2 relaxation by measuring the stereodynamics at different collision geometries. More studies seem to indicate this as a robust feature, even if we change the collision partner or change the rovibrational excitations. However, this is in contrast with the previous theoretical predictions of a more predominant l = 1 resonance within our collision temperature range. We later indeed found a l = 1 resonance in the HD-He Δj = 1 interaction, but the agreement shows up only in this case. The continuing discrepancy may point to some subtle differences in the anisotropic part of the H2-He interaction potential, but more works should be made to reach a conclusion.The study does not limit here. With the help of SARP state preparation, we are able to perform a series of experiments which investigate the effects of different vibrational excitations, different rotational excitations, as well as different collision partners. For the Δj = 2 rotationally inelastic scattering, we have studied collisions of D2 or HD, with He or Ne, and from (v = 2) or (v = 4) state. While the total cross sections may vary, we found mostly very similar l = 2 resonance characters and similar stereodynamics. For scatterings from (j = 4) to (j' = 2), however, several possible m'-states of the scattered products need to be included, leading to different angular distributions. SARP also manipulates the molecular alignments which prepares them in different incoming m-state superpositions. In particular, we prepare an exotic biaxial state where the diatom bond axis aligns simultaneously in two directions. By decomposing each axis direction separately and preparing the two corresponding uniaxial states, we are able to demonstrate an interference effect in low-energy scattering from the biaxial state. It is in analogue with a double slit where the two axis directions act as the two slits.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2023
538 $a Mode of access: World Wide Web
650 4 $a Cold. $3 560283
650 4 $a Cooling. $3 1457878
650 4 $a Lasers. $3 535503
650 4 $a Magnetic fields. $3 660770
650 4 $a Chemical reactions. $3 519248
650 4 $a Calibration. $3 2068745
650 4 $a Atoms & subatomic particles. $3 3560412
650 4 $a Molecular physics. $3 3174737
650 4 $a Quantum physics. $3 726746
650 4 $a Low temperature physics. $3 3173917
655 7 $a Electronic books. $2 lcsh $3 542853
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690 $a 0599
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710 2 $a ProQuest Information and Learning Co. $3 783688
710 2 $a Stanford University. $3 754827
773 0 $t Dissertations Abstracts International $g 84-10B.
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30363160 $z click for full text (PQDT)