Theory vs. experiment for molecular clusters: Spectra of OCS trimers and tetramers

Abstract

All singly substituted (13)C, (18)O, and (34)S isotopomers of the previously known OCS trimer are observed in natural abundance in a broad-band spectrum measured with a chirped-pulse Fourier transform microwave spectrometer. The complete substitution structure thus obtained critically tests (and confirms) the common assumption that monomers tend to retain their free structure in a weakly bound cluster. A new OCS trimer isomer is also observed, and its structure is determined to be barrel-shaped but with the monomers all approximately aligned, in contrast to the original trimer which is barrel-shaped with two monomers aligned and one anti-aligned. An OCS tetramer spectrum is assigned for the first time, and the tetramer structure resembles an original trimer with an OCS monomer added at the end with two sulfur atoms. Infrared spectra observed in the region of the OCS ν1 fundamental (≈2060 cm(-1)) are assigned to the same OCS tetramer, and another infrared band is tentatively assigned to a different tetramer isomer. The experimental results are compared and contrasted with theoretical predictions from the literature and from new cluster calculations which use an accurate OCS pair potential and assume pairwise additivity.

Rotational Spectroscopy Probes Water Flipping by Full Fluorination of Benzene

“…Thec omparison of the above data further confirms the assignment of the observed spectra. Thevalues of the oxygenring distance R Oxx = 3.05 and R OC = 3.36 for C 6 F 6 -water can be compared to the R Oxx = 3.40 and R OC = 3.60 for benzene-water.The use of the substitution structure does not require any previous assumption, [11] so the comparison clarifies how water shows adifferent orientation with respect to the two rings. [12] Forc omparison and deeper understanding of the observed structure and dynamics in the complex, ab initio calculations on C 6 F 6 -water have been performed using the GAUSSIAN09 suite of programs at MP2/6-311 ++G** level of theory.…”

First infrared investigations of OCS–H2O, OCS–(H2O)2, and (OCS)2–H2O complexes isolated in solid neon: Highlighting the presence of two isomers for OCS–H2O

“…The infrared absorptions of the H 2 O monomer, dimer, and trimer trapped in solid neon are well known for the fundamental modes, and for many overtones and combinations. 23,24 Few studies 25,26 have been done on the OCS monomer in matrix, and the only available experimental data on the OCS dimer [15][16][17] and trimer 27,28 were obtained by the McKellar group in a supersonic slit-jet expansion of a He/OCS gas mixture probed with a tunable diode laser in the region of the C-O fundamental stretching mode.…”

VMS-Rot: A New Module of the Virtual Multifrequency Spectrometer for Simulation, Interpretation, and Fitting of Rotational Spectra

“…To this purpose, a number of programs for the assignment of rotational spectra has been proposed over the years (see, e.g., ref 11), and the subject is still of great interest to the spectroscopic community. 12−14 Remarkable examples of powerful and general-purpose rotational spectroscopy softwares are the AUTOFIT program, 15 which allows an almost automatic assignment of broadband microwave (MW) spectra featuring complex molecular systems and/or conformational mixtures, 16,17 together with PGOPHER 12,18 and the widely used AABS 19 and JB95 20 packages for the analysis and fitting of rotational spectra. However, when challenging cases, e.g., showing high density of lines in the spectra, are to be dealt with, a significant step forward would be represented by the availability of computer programs that combine efficient assignment tools with accurate quantumchemical predictions of the spectroscopic parameters of interest.…”