OVERTONE VIBRATIONAL SPECTROSCOPY AND DYNAMICS IN H2_2-H2_2O COMPLEXES: A COMBINED THEORETICAL AND EXPERIMENTAL STUDY

Author Institution: JILA, University of Colorado and National Institute of; Standards and Technology, Boulder, Colorado; CNRS-Universite de Bourgogne, Dijon, France; CNRS, Institut de Planetologie et d'Astrophysique de Grenoble, France; Radboud University, 6525 AJ Nijmegen, The NetherlandsH$_2$ is the most abundant molecule in the universe and also H$_2$O occurs in relatively high concentrations in various interstellar environments. Processes that occur through the interaction of these molecules may, for example, play a role in the mechanism producing the observed H$_2$O maser activity. Spectroscopic studies of the H$_2$-H$_2$O complex in different stable and metastable states will be reported in the accompanying talk; theoretical studies will be presented here. The latter involve calculations of the bound rovibrational levels of the complex with both monomers in their vibrational ground state, as well as of the metastable levels with H$_2$O in its OH stretch overtone state, on the appropriate \textit{ab initio} five-dimensional intermolecular potential surfaces. Also the line strengths of all the allowed transitions between these levels that may occur in combination with the $v_{\rm OH} = 2 \leftarrow 0$ overtone transition were computed, for all four ortho/para H$_2$ and ortho/para H$_2$O variants of the complex. The spectrum simulated with these data agrees very well with the measured spectrum and was used to assign this spectrum. In addition, the information obtained from the theory was useful to understand the observed predissociation dynamics of the complex

Overtone vibrational spectroscopy in h-2-h2o complexes: A combined high level theoretical ab initio, dynamical and experimental study

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Nuclear spin/parity dependent spectroscopy and predissociation dynamics in v(OH)=2 <- 0 overtone excited Ne-H2O clusters: Theory and experiment

Vibrationally state selective overtone spectroscopy and state- and nuclear spin-dependent predissociation dynamics of weakly bound ortho- and para-Ne-H2O complexes (D0(ortho) = 34.66 cm-1 and D0(para) = 31.67 cm-1) are reported, based on near-infrared excitation of van der Waals cluster bands correlating with vOH = 2 ← 0 overtone transitions (|02-〉 and |02+〉) 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 potential energy surface [CCSD(T)/VnZf12 (n = 3, 4)], corrected for basis set superposition error and extrapolated to the complete basis set (CBS) limit, are employed to successfully predict and assign Π-Σ, Σ-Σ, and Σ-Π infrared bands in the spectra, where Σ or Π represent approximate projections of the body-fixed H2O angular momentum along the Ne-H2O internuclear axis. IR-UV pump-probe experimental capabilities permit real-time measurements of the vibrational predissociation dynamics, which indicate facile intramolecular vibrational energy transfer from the H2O vOH = 2 overtone vibrations into the VdWs (van der Waals) dissociation coordinate on the τprediss = 15-25 ns time scale. Whereas all predicted strong transitions in the ortho-Ne-H2O complexes are readily detected and assigned, vibrationally mediated photolysis spectra for the corresponding para-Ne-H2O bands are surprisingly absent despite ab initio predictions of Q-branch intensities with S/N > 20-40. Such behavior signals the presence of highly selective nuclear spin ortho-para predissociation dynamics in the upper state, for which we offer a simple mechanism based on Ne-atom mediated intramolecular vibrational relaxation in the H2O subunit (i.e., |02±〉 → {|01±〉; v2 = 2}), which is confirmed by the ab initio energy level predictions and the nascent OH rotational (N), spin orbit (Π1/2,3/2), and lambda doublet product distributions.status: publishe

Nuclear spin/parity dependent spectroscopy and predissociation dynamics in v(OH)=2 &lt;- 0 overtone excited Ne-H2O clusters: Theory and experiment

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Near infrared overtone (v(OH)=2 <- 0) spectroscopy of Ne-H2O clusters

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.status: publishe

Near infrared overtone spectroscopy of Ne-H2O clusters

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 (SCOPUS: ar.jinfo:eu-repo/semantics/publishe