First-Principles Molecular Dynamics Simulations of Infrared and Raman Vibrational Spectra of H5O2 +, D5O2 +, DH4O2 +, and D4HO2 + from 50 to 300 K

TL;DR

This paper uses simulations to study the vibrational spectra of water cluster ions at different temperatures, revealing new insights into their structural prevalence.

Contribution

The study provides new temperature-dependent insights into the O···O stretch region and isotopologue prevalence using first-principles simulations.

Findings

DH4O2+ (ext) is at least 90% prevalent between 50–300 K due to low zero-point energy.

D4HO2+ (ext) becomes dominant over D4HO2+ (int) at 84.9 K and higher, contrary to previous assumptions.

Rovibrational thermal averaging helps clarify complex spectra of partially deuterated isotopologues.

Abstract

We report molecular
dynamics simulations of infrared (IR) and Raman
spectra of H5O2
+ and its deuterium-substituted
analogs. We use the well-tested HBB potential and dipole surfaces
along with a recently fitted polarizability surface of CCSD­(T)/aug-cc-pVTZ
quality. The focus of the present work is to provide new insights
into the O···O stretch region, located in the [500–700]
cm–1 spectral range, by means of analyzing the spectra
over a broad range of temperatures: from 50 to 300 K. Also, rovibrational
thermal averaging was performed to untangle the unusually complex
spectra of partially deuterated isotopologues DH4O2
+ and D4HO2
+ with
H and D minority species in both internal (int) and external (ext)
positions. Our findings show that DH4O2
+ (ext) is at least 90% prevalent at the [50–300] Kelvin
temperatures, predominantly due to its low zero-point energy (ZPE).
Furthermore, contrary to previous reports that the mixed isotopologue
D4HO2
+ (int) should be favored over
D4HO2
+ (ext) due to its lower ZPE,
the present calculations indicate that while the D4HO2
+ (ext) species is “invisible” at
lower temperatures, it overtakes D4HO2
+ (int) as the dominant species at 84.9 K and higher.

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