Preparation of oriented and aligned H2 and HD by stimulated Raman pumping

Abstract

Stimulated Raman pumping has been used to prepare oriented and aligned samples of H(2)(nu=1,J=1,2,3) and HD(nu=1,J=2) under collision-free conditions using the (1,0) S(0), S(1), Q(1), Q(2), and O(3) lines. The M-sublevel anisotropies were interrogated by polarized [2+1] resonance-enhanced multiphoton ionization via the (0,1) O(2), O(3), and S(1) lines of the E,F (1)Sigma(g) (+)-X (1)Sigma(g) (+) system. The optical excitation schemes employed in this study generate highly oriented and aligned molecular ensembles. We show that the H(2)(nu=1,J=2,M=0) and H(2)(nu=1,J=2,M=2) samples retain their initial polarization for greater than 100 ns and are therefore suitable candidates for targets or projectiles in future scattering experiments.

Communication: Transfer of more than half the population to a selected rovibrational state of H2 by Stark-induced adiabatic Raman passage

“…Using SARP with partially overlapping pump (532 nm) and Stokes (699 nm) pulses we have also measured a 60% ± 6% transfer of the (v = 0, J = 0) ground state population to the H 2 (v = 1, J = 2, M = 0) state. These experimental results are a significant improvement over the transfer of only a few percent which has been previously recorded 9,24 for isolated H 2 or D 2 molecules under collision-free conditions. These results could be improved by using a molecular beam apparatus with better molecular beam collimation.…”

“…[1][2][3][4][5] Consequently, there is great interest in methods that could potentially be used to prepare a large number of isolated H 2 molecules in a single, metastable (v, J, M) quantum state; where v and J are the vibrational and rotational quantum numbers for the gasphase molecule and M is the projection of the angular momentum vector, J, along a chosen symmetry axis of the collision system. [6][7][8][9] Although stimulated Raman adiabatic passage (STIRAP) 10 and Stark chirped two-photon, or Raman adiabatic passage (SCRAP), [11][12][13][14][15][16] might be thought of as appropriate methods for transferring population between rovibrational eigenstates of H 2 , they require a suitably resonant, or near resa) N. Mukherjee 2 , or any other molecule having a wide energy bandgap between the ground and excited electronic levels, STIRAP or SCRAP will require the use of vacuum ultraviolet (VUV) or extreme ultraviolet (XUV) pulses, making it difficult to realize in practice. Moreover, in the presence of an intermediate vibronic resonance, the short wavelength pulses may cause significant ionization or dissociation of the molecule.…”

Ultrafast Angular Momentum Orientation by Linearly Polarized Laser Fields

“…First, the AMO achieved here is solely due to interferences between the wave packets created by linearly polarized light fields. This is totally different from approaches so far adopted, in which an unbalanced population for AEM sublevels is a direct consequence of optical transitions by circularly polarized light with ÁM ¼ þ2 or À2, exclusively [10]. In other words, the previous scheme is well within the classical perspective, where the transition dipole follows the right-or left-handed rotating optical field when the rotational period matches with the characteristic time for molecular rotation.…”

“…In a classical vector model, the signed value of M corresponds to the rotational velocity around the Z axis, so an oriented system is regarded as rotating in the clockwise or counterclockwise direction. In previous studies [5,10], circularly polarized radiations had been exclusively considered as being the way to induce the helical interaction that breaks the right-or left-handed symmetry around the Z axis, which is required for the optical realization of orientation. It is noted that the molecular-axis orientation has already been reported in several studies with intense nonresonant radiation [11][12][13][14], but all of them implemented linearly polarized light, and thus were related to the angular-momentum alignment.…”

Imaging rotations and vibrations in polyatomic molecules with X-ray scattering

“…4,[14][15][16][17] The main reason for this is that the high intensity of XFELs can compensate for small X-ray scattering cross sections, albeit gas-phase scattering is also possible at synchrotrons. [18][19][20][21] An important aspect is that rapid development of alignment and orientation techniques 22 and experimental methods to prepare molecules in specific quantum states [23][24][25][26][27] makes it possible to generate highly anisotropic samples with a large fraction of identical molecules. As a consequence, the degree of thermal averaging in the data becomes small, invalidating the incoherent thermal averaging of the signal originally proposed by Debye.…”