Quantum control of isotope-selective rotational contrast for H2O/T2O in the gas phase with nonresonant laser pulses

Abstract

Isotope-selective rotational control of asymmetric-top molecules is a challenging task owing to their complex rotational dynamics. Here, we extend a simulation framework for isotope-selective rotational control to the water isotopologues H2O and T2O, and numerically identify pulse conditions that maximize isotope contrast in an equimolar gas-phase mixture driven by nonresonant, linearly polarized double pulses. We examine three characteristic rotational periods associated with ΔJ = 1 transitions from the ground state and find that TrotB+C=1/B+C provides the strongest synchronization for isotope contrast. To quantify isotope-selective rotational contrast, we define a rotational contrast metric based on the three-dimensional alignments of H2O and T2O. When the pulse delay is synchronized to TrotB+C, the metric reaches a maximum value of 1.99 at 10 K; further optimization of the pulse delay and intensity ratio increases the metric to 2.20. These results demonstrate that appreciable isotope-selective contrast can be achieved even in the H2O/T2O system, where the small polarizability anisotropy makes alignment control inherently difficult, and establish a versatile route toward isotope-selective rotational control of more complex asymmetric-top molecules.