Variational vibrational states of HCOOH

Exact quantum dynamics developments for floppy molecular systems and complexes

“…Experience shows these reduced dimensionality-models (with fixed geometrical parameters) can be useful in weakly interacting systems, 11,12,[31][32][33][34] but they can introduce large errors within bound molecules. 9 It remains a question to be explored whether the error of (a qualitatively meaningful) reduced-dimensionality model is introduced due to the lack of 'quantum coherence' of the discarded modes with the active degrees of freedom or it is rather a structural effect due to the dissection of a certain D-dimensional cut of the full-dimensional PES corresponding to some fixed coordinate values.…”

CH4·F− revisited: full-dimensional ab initio potential energy surface and variational vibrational states

“…Vibrational computations of high(er)-dimensional molecular systems with floppy modes have been challenging due to the dimensionality and poor separability of the problem, and in general, due to the exponential scale-up of exact quantum dynamics methodologies with the number of the coupled vibrational degrees of freedom. Over the past decade, development is observed in several important directions, (a) coordinate representation and the kinetic energy operator [10,11,12,13,14,15,16,17]; (b) contraction techniques [3,4,5,6,7], (c) gridpruning techniques [1,18,19,20,21,22]; (d) collocation [23,24,25]; and (e) PES representation for high-dimensional quantum dynamics [26,27,28]; and (f) highly parallel computation of millions of states [29,30,31]. Methodological progress makes it possible to attenuate the exponential scale-up, including systems with large-amplitude motions [1,21,32].…”

Intramolecular Vibrational Redistribution in Formic Acid and its Deuterated Forms

“…Formic acid (HCOOH) is the simplest molecule that contains a carboxylic acid functional group and it is also one of the simplest molecules that exhibits isomerism between two planar structures. Besides the chemistry-oriented interests in its reactivity, formic acid serves as a benchmark molecule for isolated systems of this class both in theoretical studies [1][2][3][4][5] and experiments. [6][7][8] Formic acid is found in the Earth's atmosphere [9][10][11][12] and in the interstellar medium, where it was first detected in 1971 by Zuckerman et al 13 Its spectral and dynamical characteristics are of particular interest given the existence of two conformational isomers, i.e., trans-and cis-formic acid.…”

“…23 Such interactions also enabled the recent observation of both conformers of formic acid in aqueous solution at room temperature by Giubertoni et al 24 The isomerisation mechanism of formic acid from the trans to the cis isomer has already drawn attention in the past. 5,[25][26][27][28][29] Intramolecular vibrational redistribution (IVR) should play an important role in the isomerisation mechanism in the gas phase to bring the energy deposited in a bright (infrared-active) vibrational mode, e.g., by laser excitation, towards the torsional degree of freedom that mainly characterises the isomerization pathway. Observations of such an isomerism were limited to matrix-isolated formic acid and most probably assisted by the local environment since the IVR depends strongly on mode couplings.…”

“…MCTDH has already been used successfully to describe IVR in tetra-atomic molecules involving motions of large amplitude including isotopic effects, e.g., for HONO [43][44][45] and HFCO. [46][47][48] Recently, Martín Santa Daría et al 5 have predicted mixed cis-trans states that have an energy close to that of the isomerization barrier. However, to the best of our knowledge, no large-amplitude stable torsional vibrational states have ever been reported for formic acid.…”