Velocity selected laser polarization spectroscopy: a powerful and versatile method of obtaining the state-to-state differential cross section

Wilson, R.; McCaffery, A. J.

doi:10.1016/0009-2614(96)00894-9

Cited by 6 publications

(6 citation statements)

References 8 publications

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“…In recent years various novel techniques have been developed to probe the orientation of a molecule following a collision. These include the observation of fluorescence from crossed beams (one beam is the molecular sample under investigation and the other is the collision partner), 29,30 polarization spectroscopy wherein the depolarization of the molecule is probed after the collision by a pulsed laser, 23,[31][32][33][34][35][36][37][38][39] and Zeeman quantum beat spectroscopy. 40,41 A comparison between these latter two methods was made in Ref.…”

Section: Introductionmentioning

confidence: 99%

Collisional transfer of population and orientation in NaK

Wolfe

Ashman

Bai

et al. 2011

The Journal of Chemical Physics

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Collisional satellite lines with |ΔJ| ≤ 58 have been identified in recent polarization spectroscopy V-type optical-optical double resonance (OODR) excitation spectra of the Rb(2) molecule [H. Salami et al., Phys. Rev. A 80, 022515 (2009)]. Observation of these satellite lines clearly requires a transfer of population from the rotational level directly excited by the pump laser to a neighboring level in a collision of the molecule with an atomic perturber. However to be observed in polarization spectroscopy, the collision must also partially preserve the angular momentum orientation, which is at least somewhat surprising given the extremely large values of ΔJ that were observed. In the present work, we used the two-step OODR fluorescence and polarization spectroscopy techniques to obtain quantitative information on the transfer of population and orientation in rotationally inelastic collisions of the NaK molecules prepared in the 2(A)(1)Σ(+)(v' = 16, J' = 30) rovibrational level with argon and potassium perturbers. A rate equation model was used to study the intensities of these satellite lines as a function of argon pressure and heat pipe oven temperature, in order to separate the collisional effects of argon and potassium atoms. Using a fit of this rate equation model to the data, we found that collisions of NaK molecules with potassium atoms are more likely to transfer population and destroy orientation than collisions with argon atoms. Collisions with argon atoms show a strong propensity for population transfer with ΔJ = even. Conversely, collisions with potassium atoms do not show this ΔJ = even propensity, but do show a propensity for ΔJ = positive compared to ΔJ = negative, for this particular initial state. The density matrix equations of motion have also been solved numerically in order to test the approximations used in the rate equation model and to calculate fluorescence and polarization spectroscopy line shapes. In addition, we have measured rate coefficients for broadening of NaK 3(1)Π ← 2(A)(1)Σ(+)spectral lines due to collisions with argon and potassium atoms. Additional broadening, due to velocity changes occurring in rotationally inelastic collisions, has also been observed.

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Section: Introductionmentioning

confidence: 99%

Collisional transfer of population and orientation in NaK

Wolfe

Ashman

Bai

et al. 2011

The Journal of Chemical Physics

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“…those in which velocity and state selection and detection are achieved using laser spectroscopic methods. Two related techniques have now been reported: velocity-selected double resonance (VSDR) [4] and velocity-selected laser polarization (VSLP) spectroscopy [3]. In each of these methods, angular distributions are extracted from high-resolution, double-resonance lineshapes.…”

Section: Methodsmentioning

confidence: 99%

“…Here our purpose is to give a fuller description of the VSLP method briefly outlined in a recent publication [3] and to demonstrate that it yields the state to state DCS reliably in the case of Na 2 -rare-gas collisions. This is done by comparing results with those obtained by more traditional crossed-beam methods, an approach of particular significance in the context of the finding [1], that vector relations governing the conversion of linear to angular momentum exert a controlling influence on state-to-state scattering.…”

Section: Methodsmentioning

confidence: 99%

“…This has particular relevance in the context of the recent finding by McCaffery and Wilson (MW) [1] that classical vector relations constitute the 'coarse-graining' that underlies quantum complexity in collisional processes and provides a very simple predictor of scattering outcomes in the case of rotationally inelastic Li * 2 -Xe collisions. The method we describe here has been reported in preliminary form [3]. It is based on laser polarization spectroscopy (LPS), and represents a significant enhancement of the range of techniques available, since the DCS may be measured for molecules in their ground or their excited states.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Evidence for hybrid classical - quantal behaviour in state- and angle-resolved atom - diatom scattering

McCaffery¹,

Wilson²

1997

J. Phys. B: At. Mol. Opt. Phys.

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We present measurements of the state-to-state differential scattering cross section (DCS) for X 1 + g Na 2 with Xe using a new sub-Doppler spectroscopic method and compare results with those obtained using molecular beam techniques on the same system; the agreement is good. Criteria for comparison are based on the recent finding (McCaffery A J and Wilson R J 1996 Phys. Rev. Lett. 77 48) that simple quasiclassical vector relations determine the direction of the initial relative velocity vector and the scattering angle. The incident velocity direction is such that the perpendicular component just opens the inelastic channel and the parallel component is scattered. The relationship is Newtonian but is modified by the molecule's characteristic quantum structure. Angular distributions from a range of experiments are found to obey the vector relation, suggesting that atom-molecule collisions are controlled by a quantum-modified Newtonian mechanics, the modification arising as a consequence of the internal energy level structure of the molecule. We introduce the term quantum-constrained kinematics to describe the hybrid mechanics and suggest that this may also influence other collisional events.

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“…For example, the inherent velocity selection afforded by QCLs can be combined with two colour polarization spectroscopy to provide information about state-to-state differential scattering cross-sections for both elastic and inelastic collisions of vibrationally excited molecules in their ground electronic state, and to measure the degree of polarization retention during inelastic energy transfer. 23,24…”

Section: Amplitude Modulating the Pump Pulse: Decay Of The Transiementioning

confidence: 99%

Pump and probe spectroscopy with continuous wave quantum cascade lasers

Kirkbride

Causier

Dalton

et al. 2014

The Journal of Chemical Physics

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This paper details infra-red pump and probe studies on nitric oxide conducted with two continuous wave quantum cascade lasers both operating around 5 μm. The pump laser prepares a velocity selected population in a chosen rotational quantum state of the v = 1 level which is subsequently probed using a second laser tuned to a rotational transition within the v = 2 ← v = 1 hot band. The rapid frequency scan of the probe (with respect to the molecular collision rate) in combination with the velocity selective pumping allows observation of marked rapid passage signatures in the transient absorption profiles from the polarized vibrationally excited sample. These coherent transient signals are influenced by the underlying hyperfine structure of the pump and probe transitions, the sample pressure, and the coherent properties of the lasers. Pulsed pump and probe studies show that the transient absorption signals decay within 1 μs at 50 mTorr total pressure, reflecting both the polarization and population dephasing times of the vibrationally excited sample. The experimental observations are supported by simulation based upon solving the optical Bloch equations for a two level system.

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Velocity selected laser polarization spectroscopy: a powerful and versatile method of obtaining the state-to-state differential cross section

Cited by 6 publications

References 8 publications

Collisional transfer of population and orientation in NaK

Collisional transfer of population and orientation in NaK

Evidence for hybrid classical - quantal behaviour in state- and angle-resolved atom - diatom scattering

Pump and probe spectroscopy with continuous wave quantum cascade lasers

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