Infrared spectrum of CH3CN–HCl in solid neon, and modeling matrix effects in CH3CN–HCl and H3N–HCl

Abstract

Several IR bands for two isotopic forms of the CH3CN-HCl complex have been measured in neon matrices at 6 K. Assigned bands for the primary isotopomer include the CC band at 926 cm-1 , HCl the band at 2677 cm-1 , and the CN band, which occurs as a doublet at 2308/2279 cm-1. The observed frequencies are reasonably consistent with previous observations in solid argon and/or nitrogen, with the exception of HCl bands, which differed, and were ultimately found to shift systematically across various condensed-phase media. A plot of medium-induced shifts for the HCl band vs. polarizability of the host substances is essentially continuous; except for the N2-matrix frequency, for which the shift is considerably larger than that expected on this basis. In an effort to clarify the physical underpinnings of these shifts, and their structural implications, a computational study was undertaken, which examined CH3CN-HCl as well as H3N-HCl; a system for which analogous frequency shifts have been observed and characterized previously. Beyond equilibrium structure and frequency calculations, which predict that the ammonia complexes is stronger and undergoes a greater degree of structural change in bulk, condensed-phase media, the N-Cl potentials of both complexes were mapped in the gas-phase and in bulk, dielectric media. The predicted medium effects on these potentials are consistent with observations. The CH3CN-HCl curves shift slightly in response to the medium, consistent with a subtle enhancement of the hydrogen bond, and relatively small frequency shifts. The effects of the dielectric media on H3N-HCl are more substantial, and indicate significant degree of proton transfer, even for low-dielectric environments, which is constant with the extreme spectral shifts noted previously for this system.

Structural and Energetic Properties of Haloacetonitrile–BCl3 Complexes: Computations and Matrix-IR Spectroscopy

“…In the end, our efforts to observe the metastable, long-bond structures in these and earlier experiments were hampered by several factors. For one, H-bonded nitrile complexes, formed from impurity HCl resulting from BCl 3 decomposition and/or hydrolysis, have frequency shifts that are comparable to the long-bond BCl 3 systems. , Thus, the nitrile-based vibrational bands would be difficult to distinguish in the presence of any significant HCl impurity. As for observations of the BCl 3 -localized modes, the mixed isotopic composition of BCl 3 (noted above) makes the strong BCl 3 asymmetric stretching band of uncomplexed BCl 3 quite broad, such that the predicted shift for the analogous long-bond complex bands does not surpass the width of the free BCl 3 peak.…”

Twenty years of exceptional success: The molecular education and research consortium in undergraduate computational chemistry (MERCURY)

“…The faculty published 2 peer‐reviewed books, [ 238,239 ] 9 peer‐reviewed book chapters, [ 240–248 ] and 115 peer‐reviewed research papers. [ 249–363 ] This comes to 1.6 peer‐reviewed products/faculty/year during the 3‐year grant period, which is 3.2 times the rate of publication for natural science faculty at PUIs. [ 46 ]…”

“…James Phillips's research: The Phillips group studies condensed‐phase effects on the structural properties of molecular complexes: primarily electron donor‐acceptor systems (eg, CH 3 CN‐BF 3 ), [ 392,393 ] and hydrogen‐bonded/proton transfer systems. [ 273 ] Using low‐temperature IR spectroscopy, they assess the extent of structural change across various media via measured frequency shifts. Computations are vital for characterizing gas‐phase systems and providing direct insight into the mechanism for medium‐induced structural change [ 181,213,393 ] and to enable them to identify promising targets and focus their experimental efforts.…”

Experimental setup for the growth of solid crystals of inert gases for particle detection

“…The dopant is then said to be isolated within the matrix and the guests atoms can be treated as free particles. This technique has been largely applied to study the spectra of a great number of stable and unstable atomic 4,5 and molecular [6][7][8] species with the advantage of higher density with respect to spectroscopic studies in the gas phase. Recently this kind of materials have been also applied in different fields of physics both for fundamental studies and for applications.…”