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Spectra of mixed H/D water dimers are studied in the mid-infrared region of the O–D stretch fundamental (2630–2800 cm−1) using a pulsed supersonic slit jet and a tunable optical parametric oscillator infrared source. Over 30 bands, belonging to nine of the ten possible isotopologues (only H2O–HOD is missed), are observed and analyzed. The implications for excited state tunneling splittings, lifetime effects, and vibrational shifts are discussed. These are the first significant new experimental results on (gas phase) mixed water dimers in over 25 years, and they are valuable for testing water dimer theoretical calculations, a field which continues to be of lively current interest. [ABSTRACT FROM AUTHOR]

The O–D stretch fundamental region of the deuterated water dimer, (D2O)2, is further studied using a pulsed supersonic slit jet and a tunable optical parametric oscillator infrared source. The previously unobserved acceptor symmetric O–D stretch fundamental vibration is detected, with Ka = 0 ← 0 and 1 ← 0 sub-bands at about 2669 and 2674 cm−1, respectively. The analysis indicates that the various water dimer tunneling splittings generally decrease in the excited vibrational state, similar to the three other previously observed O–D stretch fundamentals. Two new (D2O)2 combination bands are observed, giving information on intermolecular vibrations in the excited O–D stretch states. The likely vibrational assignments for these and a previously observed combination band are discussed. [ABSTRACT FROM AUTHOR]

We present the observation of the N2–H2O van der Waals complex in the 2OH stretch overtone region. The high-resolution jet cooled spectra were measured using a sensitive continuous wave cavity ringdown spectrometer. Several bands were observed and vibrationally assigned in terms of ν1, ν2, and ν3, the vibrational quantum numbers of the isolated H2O molecule, as ( ν 1 ′ ν 2 ′ ν 3 ′ ) ← ( ν 1 ″ ν 2 ″ ν 3 ″ ) = (200) ← (000) and (101) ← (000). A combination band involving the excitation of the in-plane bending motion of N2 and the (101) vibration of water is also reported. The spectra were analyzed using a set of four asymmetric top rotors, each associated with a nuclear spin isomer. Several local perturbations of the (101) vibrational state were observed. These perturbations were assigned to the presence of the nearby (200) vibrational state and to the combination of (200) with intermolecular modes. [ABSTRACT FROM AUTHOR]

The weakly bound dimer water–carbon disulfide is studied by ab initio structure theory and high-resolution infrared spectroscopy. The calculations yield three stable minima in the potential energy surface, all planar. The most stable, isomer 1, was observed previously by microwave spectroscopy. It has C2v symmetry, an S–O bond, and a linear O–S–C–S backbone. Isomer 2, the next most stable, has not been considered previously by theory or experiment. It also has C2v symmetry, but with a side-by-side structure. Isomer 3, which is slightly less stable, is side-by-side with one O–H bond pointing toward an S atom. The first gas phase water–CS2 infrared spectra are reported. For isomer 1, H2O–, HDO–, and D2O–CS2 are observed in the CS2ν1 + ν3 region, H2O–CS2 in the H2O ν2 bend region, and D2O–CS2 in the D2O ν1 and ν3 stretch regions. The latter ν3 spectrum enables an experimental determination of the A rotational parameter, which turns out to be larger than expected. The new isomer 2 is observed by means of a band in the H2O ν2 region, confirming its C2v symmetry and calculated structure. [ABSTRACT FROM AUTHOR]

Spectra of rare gas atom clusters containing a single carbon dioxide molecule are observed using a tunable mid-infrared (4.3 µm) source to probe a pulsed slit jet supersonic expansion. There are relatively few previous detailed experimental results on such clusters. The assigned clusters include CO2–Arn with n = 3, 4, 6, 9, 10, 11, 12, 15, and 17, and CO2–Krn and CO2–Xen with n = 3, 4, and 5. Each spectrum has (at least) a partially resolved rotational structure, and each yields precise values for the shift of the CO2 vibrational frequency (ν3) induced by the nearby rare gas atoms, together with one or more rotational constants. These results are compared with theoretical predictions. The more readily assigned CO2–Arn species tend to be those with symmetric structures, and CO2–Ar17 represents completion of a highly symmetric (D5h) solvation shell. Those not assigned (e.g., n = 7 and 13) are probably also present in the observed spectra but with band structures that are not well-resolved and, thus, are not recognizable. The spectra of CO2–Ar9, CO2–Ar15, and CO2–Ar17 suggest the presence of sequences involving very low frequency (≈2 cm−1) cluster vibrational modes, an interpretation which should be amenable to theoretical confirmation (or rejection). [ABSTRACT FROM AUTHOR]

Weakly bound CO2-Rg2 trimers are studied by high-resolution (0.002 cm−1) infrared spectroscopy in the region of the CO2 ν3 fundamental band (≈2350 cm−1), using a tunable optical parametric oscillator to probe a pulsed supersonic slit jet expansion with an effective rotational temperature of about 2 K. CO2–Ar2 spectra have been reported previously, but they are extended here to include Rg = Ne, Kr, and Xe as well as new combination and hot bands. For Kr and Xe, a unified scaled parameter scheme is used to account for the many possible isotopic species. Vibrational shifts of CO2-Rg2 trimers are compared to those of CO2-Rg dimers, and in all cases the trimer shifts are slightly more positive (blue-shifted) than expected on the basis of linear extrapolation from the dimer. Combination bands directly measure an intermolecular vibrational mode (the CO2 rock) and give values of about 32.2, 33.8, and 34.7 cm−1 for CO2–Ar2, –Kr2, and –Xe2. Structural parameters derived for CO2-Rg2 trimers are compared with those of CO2-Rg and Rg2 dimers. Spectra of the mixed trimers CO2-Rg-He are also reported. [ABSTRACT FROM AUTHOR]

Spectra of rare gas (Rg) – D2O dimers (Rg = Ar, Kr, Xe) are studied in the region of the D2O ν3 asymmetric stretch (≈2800 cm−1), using a rapid-scan tunable infrared optical parametric oscillator source to probe a pulsed supersonic slit jet expansion. Three bands are observed in each case, labelled according to the D2O rotational transition with which they correlate as: Σ(101) ← Σ(000), Π(101) ← Σ(000), and Σ(000) ← Σ(101). The Ar-D2O bands exhibit various perturbations and line broadening effects. For Kr-D2O, the Π(101) ← Σ(000) and Σ(000) ← Σ(101) bands are simple and relatively unperturbed with almost no resolved Kr isotope structure, while the Σ(101) ← Σ(000) band is highly perturbed and shows large isotope splittings. This latter perturbation is analyzed in detail with good results. For Xe-D2O, the experimental spectra are unfortunately weaker. Analysis of the Π(101) ← Σ(000) and Σ(000) ← Σ(101) bands is again relatively straightforward, but the Σ(101) ← Σ(000) band is even more perturbed than for Kr-D2O and its analysis proves impossible. Line broadening (for Ar-D2O) and vibrational frequency shift effects are described. [ABSTRACT FROM AUTHOR]

The O–D stretch rovibrational spectra of N2–D2O and N2–DOH were measured and analyzed. A combination band involving the in-plane N2 bending vibration was also observed. These bands were recorded using a pulsed-slit supersonic jet expansion and a mid-infrared tunable optical parametric oscillator. The spectra were analyzed by considering the feasible tunneling motions, and transitions were fitted to independent asymmetric rotors for each tunneling state. The rotational constants of the four tunneling components of N2–D2O were retrieved for the excited vibrational states. A two order of magnitude increase in the tunneling splittings is observed for the asymmetric O–D stretch (ν3 in D2O) excitation compared to the symmetric stretch (ν1 in D2O) and to the ground vibrational state. This last finding indicates that the ν3 vibrational state is likely perturbed by a combination state that includes ν1. Finally, the observation of a local perturbation in the ν3 vibrational band, affecting the positions of few rovibrational levels, provides an experimental lower limit of the dissociation energy of the complex, D0 > 120 cm−1. [ABSTRACT FROM AUTHOR]

We extend studies of micro-solvation of carbon monoxide by a combination of high-resolution IR spectroscopy and ab initio calculations. Spectra of the (H2O)4–CO and (D2O)4–CO pentamers are observed in the C–O stretch fundamental region (≈2150 cm−1). The H2O containing spectrum is broadened by predissociation, but that of D2O is sharp, enabling detailed analysis that gives a precise band origin and rotational parameters. Ab initio calculations are employed to confirm the assignment to (water)4–CO and to determine the structure in which the geometry of the (water)4 fragment is a cyclic ring very similar to the isolated water tetramer. The CO fragment is located "above" the ring plane, with a partial hydrogen bond between the C atom and one of the "free" protons (deuterons) of the water tetramer. Together with the previous results on D2O–CO, (D2O)2–CO, and (D2O)3–CO, this represents a probe of the four initial steps in the solvation of carbon monoxide at a high resolution. [ABSTRACT FROM AUTHOR]

Infrared spectra of the CO2–N2 dimer are observed in the carbon dioxide ν3 asymmetric stretch region (≈2350 cm−1) using a tunable infrared optical parametric oscillator to probe a pulsed slit jet supersonic expansion. Previous results for the b-type fundamental band are extended to higher values of Ka. An a-type combination band involving the lowest in-plane intermolecular bending mode is observed. This yields a value of 21.4 cm−1 and represents the first experimental determination of an intermolecular mode for CO2–N2. This intermolecular frequency is at odds with the value of 45.9 cm−1 obtained from a recent 4D intermolecular potential energy surface. In addition, two weak bands near 2337 cm−1 are assigned to the CO2 hot band transition (v1, v2l2, v3) = (0111) ← (0110). They yield a value of 2.307 cm−1 for the splitting of the degenerate CO2 ν2 bend into in-plane and out-of-plane components due to the presence of the nearby N2. The in-plane mode lies at a lower energy relative to the out-of-plane mode. [ABSTRACT FROM AUTHOR]

The fundamental O–D stretch region (2600–2800 cm−1) of the fully deuterated water dimer (D2O)2 is studied using a pulsed supersonic slit jet source and a tunable optical parametric oscillator source. Relatively high spectral resolution (0.002 cm−1) enables all six dimer tunneling components to be observed, in most cases, for the acceptor asymmetric O–D stretch, the donor free O–D stretch, and the donor bound O–D stretch vibrations. The dominant acceptor switching tunneling splittings are observed to decrease moderately in the excited O–D stretch states, to roughly 75% of their ground state values, whereas the smaller donor-acceptor interchange splittings show more dramatic and irregular decreases. Excited state predissociation lifetimes, as determined from the observed line broadening, show large variations (0.2 ≤ τ ≤ 5 ns) depending on the vibrational state, K-value, and tunneling symmetry. Another very weak band is tentatively assigned to a combination mode involving an intramolecular O–D stretch plus an intermolecular twist overtone. Asymmetric O–D stretch bands of the mixed isotopologue dimers D2O–DOH and D2O–HOD are also observed and analyzed. [ABSTRACT FROM AUTHOR]

We report observation of new infrared bands of (CS2)2 and (CS2)3 in the region of the CS2 ν1 + ν3 combination band (at 4.5 µm) using a quantum cascade laser. The complexes are formed in a pulsed supersonic slit-jet expansion of a gas mixture of carbon disulfide in helium. We have previously shown that the most stable isomer of (CS2)2 is a cross-shaped structure with D2d symmetry and that for (CS2)3 is a barrel-shaped structure with D3 symmetry. The dimer has one doubly degenerate infrared-active band in the ν1 + ν3 region of the CS2 monomer. This band is observed to have a rather small vibrational shift of −0.844 cm−1. We expect one parallel and one perpendicular infrared-active band for the trimer but observe two parallel bands and one perpendicular band. Much larger vibrational shifts of −8.953 cm−1 for the perpendicular band and −8.845 cm−1 and +16.681 cm−1 for the parallel bands are observed. Vibrational shifts and possible vibrational assignments, in the case of the parallel bands of the trimer, are discussed using group theoretical arguments. [ABSTRACT FROM AUTHOR]