title: Near infrared overtone (vOH= 2 ← 0) spectroscopy of Ne-H2O clusters.
abstract: Vibrationally state selective overtone spectroscopy and dynamics of weakly bound Ne-H2O complexes (D0(para)= 31.67 cm-1, D0(ortho)= 34.66 cm-1) are reported for the first time, based on near infrared excitation of van der Waals cluster bands correlating with vOH= 2 ← 0 overtone transitions (|02-⟩←|00+⟩ and |02+⟩←|00+⟩) out of the ortho (101) and para (000) internal rotor states of the H2O moiety. Quantum theoretical calculations for nuclear motion on a high level ab initio potential energy surface (CCSD(T)/VnZ-f12 (n = 3,4), corrected for basis set superposition error and extrapolated to the complete basis set limit) are employed for assignment of Σ←Σ,Π←Σ, and Σ←Π infrared bands in the overtone spectra, where Σ(K = 0) and Π (K = 1) represent approximate projections (K) of the body angular momentum along the Ne-H2O internuclear axis. End-over-end tumbling of the ortho Ne-H2O cluster is evident via rotational band contours observed, with band origins and rotational progressions in excellent agreement with ab initio frequency and intensity predictions. A clear Q branch in the corresponding |02+⟩fΠ(111)←eΣ(000) para Ne-H2O spectrum provides evidence for a novel e/f parity-dependent metastability in these weakly bound clusters, in agreement with ab initio bound state calculations and attributable to the symmetry blocking of an energetically allowed channel for internal rotor predissociation. Finally, Boltzmann analysis of the rotational spectra reveals anomalously low jet temperatures (Trot≈ 4(1) K), which are attributed to "evaporative cooling" of weakly bound Ne-H2O clusters and provide support for similar cooling dynamics in rare gas-tagging studies.
authors.affiliation: JILA, National Institute of Standards and Technology, University of Colorado and Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Ziemkiewicz
authors.affiliation: JILA, National Institute of Standards and Technology, University of Colorado and Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309, USA.
authors.forename: Christian
authors.initials: C
authors.lastname: Pluetzer
authors.affiliation: JILA, National Institute of Standards and Technology, University of Colorado and Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309, USA.
authors.forename: Michael
authors.identifier: 0000000306356641
authors.initials: M
authors.lastname: Wojcik
authors.affiliation: Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles, 50 av. F.D. Roosevelt, CP 160/09, 1050 Brussels, Belgium.
authors.forename: Jérôme
authors.identifier: 0000000261421509
authors.initials: J
authors.lastname: Loreau
authors.affiliation: Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors.forename: Ad
authors.identifier: 000000031856240X
authors.initials: A
authors.lastname: van der Avoird
authors.affiliation: JILA, National Institute of Standards and Technology, University of Colorado and Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Nesbitt