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Rotational Spectroscopy of p-Toluic Acid and Its 1:1 Complex With Water

Rotational Spectroscopy of p-Toluic Acid and Its 1:1 Complex With Water

Elijah G Schnitzler, Nathan A Seifert, Ignes Kusuma, Wolfgang Jäger

J Phys Chem A. 2017 Nov 16;121(45):8625-8631.

PMID: 29049883

Abstract:

The structure and internal dynamics of p-toluic acid and its 1:1 complex with water were investigated in the gas phase using chirped-pulse and cavity-based Fourier transform microwave spectroscopy. One conformer and one isomer were identified for the monomer and monohydrate, respectively. In the monohydrate, water acts as both a hydrogen bond donor and acceptor, participating in a six-membered intermolecular ring with the carboxyl group. Both a- and b-type transitions were observed for the monomer; only a-type transitions were observed for the monohydrate. Rotational transitions of both species show splittings originating from methyl internal rotation, for which the potentials include 3- and 6-fold symmetry terms of similar amplitude. For the monomer, a few b-type transitions are missing, and their intensities were found to be transferred to c-type transitions with common energy levels, which are otherwise forbidden. No splittings attributable to a water internal tunneling motion were observed for the monohydrate. Furthermore, the absence of c-type transitions in the spectrum of the monohydrate, despite the large μc dipole moment component of the equilibrium geometry obtained by ab initio calculations, is consistent with a barrierless wagging motion of the free hydrogen of water, leading to an average μc dipole moment component of zero. These results provide insights regarding the interactions between atmospheric p-toluic acid and water in prenucleation complexes and at the air-water interface of aqueous aerosols, where p-toluic acid may act as a surfactant.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP99945	p-Toluic acid		99-94-5	Price

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