Collisional transfer of population and orientation in NaK

Abstract

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.

Global analysis of data on the spin-orbit-coupledA1Σu+andBai1, Ahmed2, Beser3 et al. 2011Phys. Rev. ASelf Cite

“…A quantitative study of the transfer of population and orientation in collisions of NaK molecules with argon and potassium atoms has been carried out and reported in [58] and [59]. These references discuss the transfer of orientation following the discussion of Ref.…”

Theoretical calculations of rotationally inelastic collisions of He with NaK(A 1Σ+): Transfer of population, orientation, and alignment

“…Later in this paper, we will show that the calculated cross sections for rotational excitation reproduce the characteristic propensity for ∆ j = even transitions and also lead to estimates of the rate coefficients in reasonable agreement with experiment. 1 Additional tests of the accuracy of the calculations will be possible as further experimental results become available.…”

“…Recent experimental measurements 1 have provided detailed information about rotationally inelastic collisions of NaK (A 1 Σ + ) with noble gas perturbers. Of particular interest in this work is the measurement of the degree to which the orientation or alignment of an ensemble of rotationally excited molecules is preserved during collisions in a cell environment.…”

“…Rate coefficients for the transfer of population in collisions of various diatomic molecules with rare gas perturbers have been of interest for many years, 2 but most measurements average the transitions jm → j ′ m ′ over m and m ′ . The measurements of Wolfe et al 1 and experimental and theoretical work in other labs [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] that investigates the evolution of orientation and alignment during collisions provide a great deal of additional, detailed information about changes in m as well as j. The work presented here draws on that foundation.…”

Semiclassical model for the distribution of final polar angles and m′ states in rotationally inelastic collisions

“…Information about transitions from states jm to j ′ m ′ is critical for a detailed understanding of the collisional transfer of orientation and alignment and of the alignment of molecules by laser pulses [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Our recent calculations [20] addressed this issue; we reported fully quantum mechanical calculations for collisions of NaK (A 1 Σ + ) with He, including the Grawert coefficients [1] necessary to calculate transition cross sections σ(jm → j ′ m ′ ).…”