1 Paradoxical constitutive law between donor O -H bond length and its stretching frequency in water dimer Rui Liu1 Xinrui Yang1 Famin Yu1 and Zhigang Wang123

2025-04-28 0 0 556.89KB 10 页 10玖币

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Paradoxical constitutive law between donor O-H bond length

and its stretching frequency in water dimer

Rui Liu1, Xinrui Yang1, Famin Yu1 and Zhigang Wang1,2,3*

1Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China

2College of Physics, Jilin University, Changchun 130012, China.

3Institute of Theoretical Chemistry, Jilin University, Changchun 130023, China

*email: wangzg@jlu.edu.cn (Z. W.)

Abstract

The constitutive laws of hydrogen bonds (H-bonds) are central to understanding microphysical processes not

precisely observed, especially in terms of structural properties. Previous experiences in water H-bonding

revealed that as the intermolecular O···O distance shortens, the O-H stretching frequency redshifts; thus, an

elongated O-H bond length can be empirically inferred, which is described as the constitutive law under the

cooperative effect. Here, using the high-precision CCSD(T) method, we report a violation of the conventional

constitutive law in water dimer. That is, when the variation in the O···O distance changes from stretching by

0.06 to contracting by -0.15 Å compared to the equilibrium position, the donor O-H bond length decreases

from 0.9724 to 0.9717 Å, and the O-H stretching frequency redshifts from 3715 to 3708 cm-1. Our work

highlights that the O-H bond length decreases simultaneously with its stretching frequency, which is clearly

inconsistent with the previously recognized constitutive law.

Introduction

Constitutive laws are specific relationships that map multiple physical quantities to one another, and for

hydrogen-bonding (H-bonding, referring to X-H···Y), more attention is focused on the constitutive law between

bond length and vibrational stretching frequency.1-3 Taking the most prototypical water H-bonding as an

example, owing to the limitations of current experimental measurements and characterization techniques, it

is difficult to determine the position of the hydrogen atom with sufficient precision,4 thus direct observation of

the changes in O-H bond length below Å, or even 10-2 Å, remains a formidable challenge.5,6 Hence, the O-H

bond length can only be measured indirectly through the constitutive law between the O-H bond length and

the corresponding stretching frequency.7,8 This indicates that the constitutive law plays a decisive role in the

structural identification responsible for many developments and progress in physics over the last nearly seven

decades.9,10 In fact, this constitutive law has been now empirically well-established that an elongation of the

O-H bond length is accompanied by a red-shifted O-H stretching frequency (down-shift),11 while a shortening

of the O-H bond length corresponds to a blue-shifted O-H stretching frequency (up-shift).12,13 The law was

also theoretically depicted using various levels of theory, and the corresponding stretching frequencies were

experimentally confirmed.14-19 Of particular note, this constitutive law is considered as a criterion for defining

H-bonds,11 and is surprisingly robust across a broad variety of H-bonded systems with different H-bond

strengths, including water, ion-water and liquid water clusters, etc.20 Not only that, it has also been employed

to determine the long-standing cooperative effect,21 which is one of the most remarkable features of H-bonds.

In water dimer reproducing the structural changes of cooperative effect, this constitutive law was equivalently

established that as the O···O distance decreases, the O-H bond length increases, and the concomitant

stretching frequency redshifts.11,22,23 Nevertheless, in 2021, high-precision ab initio calculations on water dimer

revealed that as the O···O distance decreases, the O-H bond length always decreases rather than cooperatively

increasing, which is referred to as the uncooperative effect of H-bonds.24 The anomalous uncooperative effect

is further attributed to electron correlation. Given the quantum mechanical viewpoint established by the

uncooperative effect, the reliability of the constitutive law at the atomic level should be scrutinized seriously.

In this work, we use the well-accepted benchmark method of high-precision ab initio, i.e., coupled-cluster

singles and doubles with perturbative triple excitations (CCSD(T)) method, to investigate the constitutive law

in the uncooperative water dimer. In particular, detailed analyses showed that when the variation in the O···O

distance changes from a stretch of 0.06 to a contraction of -0.15 Å compared to the equilibrium position, a

previously-perceived redshift in the O-H stretching frequency corresponds to a decreased O-H bond length

arising from the uncooperative effect. That is, the O-H bond length decreases simultaneously with its stretching

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1ParadoxicalconstitutivelawbetweendonorO-HbondlengthanditsstretchingfrequencyinwaterdimerRuiLiu1,XinruiYang1,FaminYu1andZhigangWang1,2,3*1InstituteofAtomicandMolecularPhysics,JilinUniversity,Changchun130012,China2CollegeofPhysics,JilinUniversity,Changchun130012,China.3InstituteofTheoreticalChemistry...

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1 Paradoxical constitutive law between donor O -H bond length and its stretching frequency in water dimer Rui Liu1 Xinrui Yang1 Famin Yu1 and Zhigang Wang123

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