Communication: THz absorption spectrum of the CO2-H2O complex: observation and assignment of intermolecular van der Waals vibrations

Terahertz absorption spectra have been recorded for the weakly bound CO2-H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems' flat intermolecular potential energy surface. A (semi)-empirical value for the zero-point energy of 273 ± 15 cm(-1) from the class of intermolecular van der Waals vibrations is proposed and the combination with high-level quantum chemical calculations provides a value of 726 ± 15 cm(-1) for the dissociation energy D0.

Observation and rovibrational analysis of the intermolecular NH3 libration band nu9(1) of H3N-HCN

The high-resolution far-infrared absorption spectrum of the gaseous molecular complex H(3)N-HCN is recorded by means of static gas-phase Fourier transform far-infrared spectroscopy at 247 K, using a synchrotron radiation source. The spectrum contains distinct rotational structures which are assigned to the intermolecular NH(3) libration band nu9(1) (nu(B)) of the pyramidal H(3)N-HCN complex. A rovibrational analysis based on a standard semirigid symmetric top molecule model yields the band origin of 260.03(10) cm(-1), together with values for the upper state rotational constant B' and the upper state quartic centrifugal distortion constants D'(J) and D'(JK). The values for the upper state spectroscopic constants indicate that the hydrogen bond in the H(3)N-HCN complex is destabilized by 5% and elongates by 0.010 A upon excitation of a quantum of libration of the hydrogen bond acceptor molecule.

Observation and rovibrational analysis of the intermolecular HCl libration band upsilon6(1) of HCN-HCl, DCN-HCl and H13CN-HCL

The high-resolution far-infrared absorption spectrum of the intermolecular HC1 libration band upsilon6(1) (upsilonB) of the gaseous molecular complex H12CN-HCl and the two isotopically substituted species H13CN-HCl and D12CN-HCl is recorded by means of static gas-phase Fourier transform far-infrared spectroscopy at 205 K using an electron storage ring source. The rotational structure of the upsilon6(1) band has the typical appearance of a perpendicular type band of a linear polyatomic molecule. The structure is analyzed using a standard semi-rigid linear molecule model including l-type doubling to yield the band origin upsilon0, together with values for the upper state rotational constant B', the upper state quartic centrifugal distortion constant D'j and the value for the l-type doubling constant q6. The values for the ground-state spectroscopic constants B" and D"j for D12CN-H35Cl and H13CN-H35Cl are determined for the first time by ground state combination difference analyses. A number of upsilon6(1) + upsilon7(1) - upsilon7(1) and upsilon6(1) + 2upsilon7(2) - 2upsilon7(2) hot bands are observed in the spectra and the sum of the anharmonicity constants X(6,7) + g(6,7) is estimated. The observed decrease of the rotational constant B together with the simultaneous increase of the quartic centrifugal distortion constant Dj upon excitation of the HCl libration mode indicate that the hydrogen bond in the molecular complex is significantly destabilized upon intermolecular vibrational excitation. The calculated harmonic force constants for the intermolecular hydrogen bond stretching vibration upsilon(sigma) for the ground state and the excited HCl libration state indicate that the excitation of the HCl libration mode destabilizes the intermolecular interaction between HCN and HCl by almost 20%. The hydrogen bond is elongated by 0.030 A upon excitation of the upsilon6(1) mode.

The vibrational spectrum of H2O3

This report presents positive infrared spectroscopic identification of H2O3, a higher oxide of hydrogen of importance for the understanding of the chain formation ability of atomic oxygen and a possible intermediate in hydrogen oxygen radical chemistry. All fundamental vibrations of H2O3, isolated in an argon matrix, have been observed. In addition, several bands of HDO3, D2O3, and H2(16)O2(18)O have been measured. One particular mode, the antisymetric O-O stretch at 776 cm-1, should be observable even in the presence of high water concentrations.

The nu5 Band of HClO4

The high-resolution infrared spectrum of perchloric acid has been observed in the 700-750 cm-1 region using the infrared beamline at the MAX-I electron storage ring in Lund, Sweden. The spectrum displays extensive rotational structure due to a type a band and is assigned to nu5, the HO-ClO3 stretch. Approximately 1100 transitions in H35ClO4 and ca. 300 in H37ClO4 have been fitted using single subband analysis, generating constants for transitions having the same K. The origin of H35ClO4 K = 3t series is found to be 726.9971(4) cm-1. Rotationally resolved infrared line positions are now available for the identification of HClO4 in the atmosphere, which may be produced by the heterogeneous oxidation of chlorine containing species in the stratosphere. Copyright 1998 Academic Press.