J. D. Cruzan

Quantifying Hydrogen Bond Cooperativity in Water: VRT Spectroscopy of the Water Tetramer

Measurement of the far-infrared vibration-rotation tunneling spectrum of the perdeuterated water tetramer is described. Precisely determined rotational constants and relative intensity measurements indicate a cyclic quasi-planar minimum energy structure, which is in agreement with recent ab initio calculations. The O-O separation deduced from the data indicates a rapid exponential convergence to the ordered bulk value with increasing cluster size. Observed quantum tunneling splittings are interpreted in terms of hydrogen bond rearrangements connecting two degenerate structures.

Vibration-Rotation Tunneling Spectra of the Water Pentamer: Structure and Dynamics

Far-infrared laser vibration-rotation tunneling spectroscopy was used to measure an intermolecular vibration (81.19198 wave numbers) of the isolated water (D2O) pentamer. Rotational analysis supports the chiral, slightly puckered ring structure predicted by theory. The experimentally deduced interoxygen separations for the water clusters up to the pentamer showed exponential convergence toward the corresponding distance in bulk phase water.

Vibrational and K’a dependencies of the multidimensional tunneling dynamics in the 82.6 cm−1 intermolecular vibration of the water dimer‐d4

Using tunable far infrared laser absorption spectroscopy, 12 vibration–rotation‐tunneling (VRT) subbands, consisting of approximately 230 transitions have been measured and analyzed for an 82.6 cm−1 intermolecular vibration of the water dimer‐d4. Each of the VRT subbands originate from K‘a = 0 and terminate in either K’a = 0 or 1. These data provide a complete characterization of the tunneling dynamics in the vibrationally excited state as well as definitive symmetry labels for all VRT energy levels. Furthermore, an accurate value for the A’ rotational constant of 122.9 GHz is found to agree well with its corresponding ground state value. All other excited state rotational constants are fitted, and discussed in terms of the corresponding ground state constants. In this vibration, the quantum tunneling motions are determined to exhibit large dependencies with both the K’a quantum number and the vibrational coordinate, as is evidenced by the measured tunneling splittings. The generalized internal‐axis‐metho...

The far‐infrared vibration–rotation–tunneling spectrum of the water tetramer‐d8

The far‐infrared vibration–rotation–tunneling spectrum of (D2O)4 has been measured in the spectral region near 2.04 THz. Observation of additional transition doublets with a constant 5.6 MHz spacing in a parallel (c‐type) spectrum extends the first detailed study of this cluster [Science 271, 59 (1996)]. Three possibilities are explored for the origin of this small splitting: tunneling between degenerate equilibrium structures via facile torsional motions analogous to those observed in the water trimer, tunneling between nondegenerate structural frameworks, and tunneling made feasible only through excitation of a specific vibrational coordinate. The degenerate tunneling scheme best accounts for the spectral features, although the precise dynamics responsible for the observed spectral features cannot be uniquely established from the present data. A further doubling of spectral features, observed only in the K=2 manifold of transitions for J≥3, is symmetric about the unperturbed symmetric top energy levels ...

QUANTITATIVE CHARACTERIZATION OF THE (D2O)3 TORSIONAL MANIFOLD BY TERAHERTZ LASER SPECTROSCOPY AND THEORETICAL ANALYSIS

We report the measurement of two new perpendicular (D2O)3 torsional bands by terahertz laser vibration–rotation–tunneling (VRT) spectroscopy of a planar pulsed supersonic expansion. The first (28.0 cm−1) band corresponds to the k=±2l←0 transition, and is the lowest frequency vibrational spectrum observed for a water cluster. The second (81.8 cm−1) band originates in the first excited torsional state, and has been assigned as k=3u←±1l. An effective three-dimensional Hamiltonian is derived to describe the rotational structure of each torsional state. Degenerate torsional levels with k=±1 and k=±2 exhibit a Coriolis splitting linear in K implying the presence of vibrational angular momentum, and a second-order splitting from off-diagonal coupling between degenerate sublevels with +|k| and −|k|. With this effective Hamiltonian we fit a total of 554 rovibrational transitions in five different bands connecting the lowest nine torsional states, with a rms residual of 1.36 MHz. The data set comprises the two new ...

Quantitative characterization of the water trimer torsional manifold by terahertz laser spectroscopy and theoretical analysis. II. (H2O)(3)

We report the measurement of two new (H2O)3 bands by terahertz laser vibration–rotation–tunneling (VRT) spectroscopy. Both bands have been assigned to torsional (“pseudorotational”) transitions and are highly perturbed by Coriolis interactions. The 42.9 cm−1 band corresponds to the k=±2←±1 transition while the 65.6 cm−1 band corresponds to the k=±2←0 transition. A model Hamiltonian is derived which allowed a global fit of 361 VRT transitions of these two new bands and the previously reported torsional band at 87.1 cm−1. Each of the bifurcation tunneling components is accurately described. This global fit represents a complete description of the VRT transitions of (H2O)3 up to 150 cm−1, and complements our similar treatment of the (D2O)3 torsional dynamics.

Interstellar Detection of CCC and High-Precision Laboratory Measurements near 2 THz

We describe more fully our original tentative interstellar detection of the triatomic pure carbon chain molecule, CCC, in absorption toward the Galactic center source Sgr B2. C3 was detected with the Kuiper Airborne Observatory (KAO) by observing the R(2) bending vibration-rotation transition (0, 1 1 ,0 0, 0 0 , 0) near 65.7 cm 1 during one ) R ( of the last flights of KAO. The R(2) absorption line detected toward Sgr B2 is centered at 63.7(5) km s 1 , with km s 1 and a peak absorption of 18(3)%. This original tentative interstellar detection of C 3 DV(FWHM)p 8.3(9) has recently been confirmed by J. Cernicharo et al. through observation of a total of nine absorption lines, including the same R(2) line with the Infrared Space Observatory . We also present highly precise new laboratory measurements of 10 rovibrational transition frequencies of the n2 bending mode of C3, which have been obtained with the Cologne Sideband Spectrometer for Terahertz Application. Subject headings: ISM: individual (Sagittarius B2) — ISM: molecules — line: identification — methods: laboratory — techniques: spectroscopic On-line material: color figure

Far-infrared VRT spectroscopy of two water trimer isotopomers: vibrationally averaged structures and rearrangement dynamics.

We report the measurement of far-infrared vibration-rotation tunnelling parallel bands of two partially deuterated water trimer isotopomers: (D2O)2DOH and (H2O)2DOH at 97.2607 cm-1 and approximately 86 cm-1, respectively. The hydrogen bond rearrangement dynamics of the two mixed trimers can be described by the simplified molecular symmetry G8, which accounts for both the flipping and bifurcation tunnelling motions previously established for (H2O)3 and (D2O)3. The observed donor tunnelling quartet, rather than triplet, splitting indicates that the two homogeneous monomers (D2O or H2O) in each mixed trimer experience slightly different environments. Vibrationally averaged structures of (H2O)3, (D2O)3, and (D2O)2DOH were examined in a Monte Carlo simulation of the out-of-plane flipping motions of the free atoms. The simulation addresses both the symmetric top behaviour and the negative zero-point inertial defect for (H2O)3 and (D2O)3, which were insufficiently counted in all previous structure models. The average ground state O--O separations, which are correlated to other angular coordinates, were determined to be 2.84 +/- 0.01 angstroms for all three species. The simulated difference in hydrogen bond nonlinearity also supports the inequivalency of the two homogeneous monomers. The structural simulation shows that the unique H in (D2O)2DOH is free, while a torsional analysis suggests the unique D in (H2O)2DOH is bound within the cyclic ring. Both bands can be assigned to the pseudorotational transitions which correlate to those found in the pure trimers.

Terahertz laser vibration–rotation–tunneling spectrum of the water pentamer–d10.: Constraints on the bifurcation tunneling dynamics

Abstract The vibration–rotation–tunneling (VRT) spectrum of a low-frequency intermolecular vibration of (D 2 O) 5 was recorded near 0.9 THz (30.2 cm −1 ). From an analysis of the relative intensities in the compact Q-branch region, the ground-state C-rotational constant is estimated to be 975±60 MHz, consistent with ab initio structural predictions. The precisely determined B -rotational constant ( B =1750.96±0.20 MHz) agrees well with previous results. Efforts to resolve possible bifurcation tunneling fine structure, such as that observed in VRT spectra of (D 2 O) 3 , revealed no such effects. This constrains the splittings to be less than 450 kHz, or roughly 3 times smaller than required by previous results.