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Rotational coherence spectroscopy (RCS) implemented by time-resolved ionization depletion (TRID) was used to examine the structure of naphthalene trimer. Results provide evidence for a C3h structure in which three symmetrically equivalent naphthalene moieties are oriented with their long axes parallel. Results also show that the sensitivity of ionization detection coupled with the selectivity of mass analysis available through RCS-TRID permit high-resolution analysis not obtainable by other methods.

The intramolecular vibrational redistribution (IVR)-assisted ionization-gain stimulated Raman spectroscopy (IGSRS) and the jet-cooled fluorene are described. The fluorene spectra has shown extensive vibrational coupling interactions involving both the aliphatic and aromatic CH-stretching first excited states with nearby background states.

The first excited state (S1) intermolecular potential energy surface for the fluorobenzene-argon van der Waals complex is evaluated. Results are compared to the experimental data available and to those found in previous theoretical papers on ground state potentials for similar complexes.

The first excited state ([S.sub.1]) intermolecular potential energy surface for the p-difluorobenzene-Ar van der Walls complex was evaluated using the coupled-cluster method and the augmented-cc-pVDZ-3321 basis set. The results when compared to the benzene- and fuorobenzene-AR [S.sub.0] intermolecular potential energy surfaces show stronger interaction in the excited state, the dissociation energy being larger and the bond distance shorter.

The ground state intermolecular potential energy surface for the p-difluorobenzene-Ar van der Waals complex is evaluated using the coupled cluster singles and doubles including connected triple excitations [CCSD(T)] model and the augmented correlation consistent polarized valence double-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. The results clearly improve previously available data and show the importance of a good correlation method and basis set when dealing with van der Waals complexes.

The structural properties of aromatic-aromatic van der Waals complexes of the form M-X, where M = perylene or fluorene and X = benzene or toluene, were investigated using rotational coherence spectroscopy. The structure of aromatic-aliphatic hydrocarbon dimers of the form M-Y, where M = perylene or fluorene and Y = cyclohexane or methylcyclohexane, was also characterized. Experimental results showed that the rotational constants of the perylene complexes are in good agreement with centrally bound, parallel-stacked structures in which the monomer planes are separated by a distance of 3.5-4.3 A.

We report full-dimensional and fully coupled quantum calculations of the inter- and intramolecular vibrational states of three isotopologues of the hydrogen chloride-water dimer: DCl-H 2 O (DH), HCl-D 2 O (HD), and DCl-D 2 O (DD). The present study extends our recent theoretical investigation of the nine-dimensional (9D) vibrational level structure of the HCl-H 2 O (HH) dimer [Liu, Y.; Li, J.; Felker, P. M.; Bačić, Z. Phys. Chem. Chem. Phys. 2021, 23, 7101-7114]. It employs the same accurate 9D permutation invariant polynomial-neural network potential energy surface and the highly efficient bound-state methodology. The objective of this work is to elucidate the isotopologue variations of a range of bound-state properties of the hydrogen chloride-water dimer and compare them to those of the HH dimer. In order to achieve this, for the isotopologues considered, the rigorous 9D quantum calculations performed encompass all intramolecular vibrational fundamentals, and their frequency shifts relative to the isolated monomer values, together with the low-lying intermolecular vibrational states in each of the intramolecular vibrational manifolds of interest. Moreover, for the ground state of each isotopologue, several informative vibrationally averaged intermolecular geometric properties of the dimer are computed, as well as the three rotational constants. The energies of the intermolecular inversion and rock modes, which mainly involve the motions of the water moiety, differ greatly for H 2 O and D 2 O, but are much less sensitive to whether the hydrogen chloride isotopologue is HCl or DCl. On the other hand, the excitation of the HCl/DCl stretch changes significantly the energies of the water inversion and rock modes. The DCl stretch frequency shift computed in 9D for the DD dimer, -114.91 cm -1 , agrees extremely well with the corresponding experimental value of -115.20 cm -1 measured by Saykally and co-workers.

The benzene-Ar ground-state S(0) intermolecular potential energy surface is evaluated using the coupled cluster singles and doubles model including connected triple corrections and the augmented correlation consistent polarized valence triple-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. The surface is characterized by absolute minima of -390.1 cm(-1) where the argon atom is located on the benzene C(6) axis at distances of +/-3.536 A, and has a general shape close to the available ground-state S(0) and the first singlet S(1) and triplet T(1) excited-state surfaces. Using the potential, the intermolecular level structure of the complex is evaluated. The new intermolecular potential energy surface gives very accurate results and improves those previously available.

The ground state intermolecular potential energy surface for the p-difluorobenzene-Ar van der Waals complex is evaluated using the coupled cluster singles and doubles including connected triple excitations [CCSD(T)] model and the augmented correlation consistent polarized valence double-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. The surface minima are characterized by the Ar atom located above and below the difluorobenzene center of mass at a distance of 3.5290 A. The corresponding binding energy is -398.856 cm(-1). The surface is used in the evaluation of the intermolecular level structure of the complex. The results clearly improve previously available data and show the importance of using a good correlation method and basis set when dealing with van der Waals complexes.