The near-infrared vibration–rotation spectra of the weakly bound complexes HeHF, HeDF, and HeHCl are observed in a slit supersonic expansion. The spectra correspond to simultaneous excitation of vibration and internal rotation of the H(D)X subunit within the complex. The HeHF and HeDF P/R branch transitions show J-dependent excess linewidths, which are attributed to rapid predissociation of the excited states from intramolecular rotation–translation energy transfer. The corresponding P/R branch transitions in HeHCl are not observed despite good S/N on the Q branch, suggesting even more rapid predissociation for the upper state of this complex. The Q branch transitions for all three complexes abruptly terminate at low J, yielding lower limits to the number of bound rotational states and good estimates of the dissociation energies D0=7.1±0.1 cm−1 for HeHF and HeDF, and 10.1±1.2 cm−1 for HeHCl. In addition to isotropic intermolecular potentials, the HeHF/HeDF data yield considerable information on the potential anisotropy in the region sampled by the bound and quasibound states. The information so obtained is complementary to results from scattering studies and provides sensitive tests for refining trial potential energy surfaces.

Articles you may be interested inHigh resolution Fourier transform infrared spectroscopy of the ν6 and ν10 bands of jetcooled Fe(CO)5Slitjet nearinfrared diode laser spectroscopy of (DCl)2: ν1, ν2 DCl stretching fundamentals, tunneling dynamics, and the influence of large amplitude ''geared'' intermolecular rotation J. Chem. Phys. 99, 5045 (1993); 10.1063/1.466005Statespecific vibrational predissociation and interconversion tunneling quenching at 3ν1 and 3ν2 of (HF)2 J. Chem. Phys. 98, 9266 (1993); 10.1063/1.464407Direct IR laser absorption spectroscopy of jetcooled CO2HF complexes: Analysis of the ν1 HF stretch and a surprisingly low frequency ν6 intermolecular CO2 bend An extensive series of near-infrared absorption spectra are recorded for jet-cooled (6-14 K) hydrogen chloride dimer (HClh. Both lia=O and l i a = ± 1 bands are observed for both the free (VI) and bonded (V2) HCI stretches; all three chlorine isotopomers (H 35CI_H 35CI, H 35CI_H 37CI, and H 37CI_H 37Cl) are observed and analyzed for K; " 2. The slit jet spectrum extends significantly the previous cooled cell infrared study of this complex and provides a measure of tunneling splittings for Ka=O and 1 for each of the HCI ground (v=O) and excited (v= 1) states. Mode specific vibrational predissociation is observed via analysis of the absorption line shapes, with Lorentzian contributions to the line profiles of aVI :51.6 MHz and aV2=5.1 ± 1.2 (2a) MHz full width at half-maximum for VI and V2 excitation, respectively. Stronger coupling in (HClh of the bonded (V2) vs free (VI) HCI vibration to the dissociation coordinate is consistent with the comparable trends observed in other hydrogen bonded dimers. Quantum mechanical variational calculations on an electrostatic angular potential energy surface are used to model the internal HCI rotor dynamics using a coupled rotor formalism; analysis of the internal rotor eigenfunctions provides direct evidence for large amplitude "geared" internal rotation of the HCI subunits.