Molecular spectroscopy and dynamics: a polyad-based perspective

Herman, Michel; Perry, David

doi:10.1039/c3cp50463h

Cited by 56 publications

(49 citation statements)

References 392 publications

(462 reference statements)

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“…[33] In Sandorfy's modelH ,a ll hydrogen and carbon (or silicon) orbitals are considered, but it has been rarely if ever used to gain simple intuitive insight, because it is still very complex. Sandorfy model Cf or alkanes (or oligosilanes), whichc onsiders only two orbitals on each carbon (or silicon) within ac hain, is more suitable.H owever,b oth Sandorfy modelsa re oversimplified for our purposes,s incet hey give the same result for all conformations of am olecule.…”

Section: Methods and Resultsmentioning

confidence: 99%

Intuitive Understanding of σ Delocalization in Loose and σ Localization in Tight Helical Conformations of an Oligosilane Chain

Jovanović

Antic

Rooklin

et al. 2017

Chemistry An Asian Journal

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Conformational effects on the s-electron delocalization in oligosilanes are addressed by Hartree-Fock and time-dependent density functional theory calculations (B3LYP,6 -311G**) at MP2 optimizedg eometries of permethylated uniformly helical linear oligosilanes (all-w-Si n R 2n + 2 )u p to n = 16 and forb ackboned ihedral angles w = 55-1808.T he extent of s delocalization is judged by the partition ratio of the highest occupiedm olecular orbital and is reflected in the dependence of its shape and energy and of UV absorption spectra on n. The results agree with knowns pectra of all-transoid loose-helix conformers (all-[AE 165]-Si n Me 2n + 2 )a nd revealatransition at w % 908 from the "s-delocalized" limit at w = 1808 toward and closetot he physically non-realizable "s-localized" tight-helix limit w = 0w ith entirely different properties. The distinction is also obtainedi nt he Hückel Ladder Ha nd Cm odelso fs delocalization. An easy intuitive way to understand the origin of the two contrasting limits is to first view the linear chain as two subchains with alternating primary and vicinal interactions (s hyperconjugation), one consisting of the odd and the other of the even s(SiSi) bonds, andt hen allow the two subchainst oi nteract by geminal interactions (s conjugation).

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Section: Methods and Resultsmentioning

confidence: 99%

Intuitive Understanding of σ Delocalization in Loose and σ Localization in Tight Helical Conformations of an Oligosilane Chain

Jovanović

Antic

Rooklin

et al. 2017

Chemistry An Asian Journal

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“…1 Evidence for IVR in the frequency domain comes from splittings, shifts, and broadening of lines, that can lead to very rich discretely resolved spectra on one end, or poorly resolved, heavily broadened spectra on the other. 15 The transition from well resolved to heavily broadened spectra was elegantly captured by Boyarkin et al in their study focusing on highly excited vibrational states of CH 3 OH, where they found an exponential increase in the degree of broadening due to IVR in going from the 2 nd to 8 th OH stretching overtone. 16 The effect of the helium nanodroplet environment on IVR processes is expected to be modest, at most, and this is based on a previous study on the first overtone spectroscopy of chromophores in helium nanodroplets that have differing degrees of IVR, which dictates the linewidths in the gas phase.…”

Section: Introductionmentioning

confidence: 95%

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets

Douberly

Jäger

2014

The Journal of Chemical Physics

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Methanol is one of the simplest molecules that undergo torsional oscillations, and so it has been extensively studied in the gas phase by various spectroscopic techniques. At 300 K, a large number of rotational, torsional, and vibrational energy levels is populated, and this makes for a rather complicated spectrum, which is still not fully understood. It is expected that in going from 300 K to 0.4 K (the temperature of helium nanodroplets) the population distribution of methanol will mainly collapse into two states; the JK = 00 state for the A1 nuclear spin symmetry species (with ICH3 = 3/2), and the JK = 1-1 state for the E species (ICH3 = 1/2). This results in a simplified spectrum that consists of narrow a-type (ΔK = 0) lines and broader b- and c-type (ΔK = ±1) lines. We have recorded the rotovibrational spectrum of CH3OH in the OH stretching, CH3 stretching and bending, CH3 rocking, and CO stretching regions, and have firmly assigned five bands (v1, v2, v3, v7, and v8), and tentatively assigned five others (v9, 2v4, v4 + v10, 2v10, and v4 + v5). To our knowledge, the transitions we have assigned within the v4 + v10, 2v10, and v4 + v5 bands have not yet been assigned in the gas phase, and we hope that considering the very small "matrix" shift in helium nanodroplets (<1 cm(-1) for most subband origins of CH3OH), those made here can aid in their gas phase identification. Microwave-infrared double resonance spectroscopy was used to confirm the initially tentative a-type infrared assignments in the OH stretching (v1) band of A1 species methanol, in addition to revealing "warm" b-type lines. From a rotovibrational analysis, the B rotational constant is found to be reduced quite significantly (56%) with respect to the gas phase, and the torsional tunneling splittings are relatively unaffected and are at most reduced by 16%. While most rovibrational peaks are Lorentzian shaped, and those which are significantly perturbed by vibrational coupling in the gas phase are additionally broadened, the narrowest ΔJ = +1 peaks are asymmetric, and a skew-type analysis suggests that the response time of the helium solvent upon excitation is of the order of 1 ns.

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“…In addition to supporting reaction dynamics [65], including isomerization processes [66][67][68][69][70], overtone excitation is recognised as driving some of the atmospheric chemistry [71][72][73] and as controlling bond selected chemistry [74,75]. The investigation of overtones generated the local mode theory [76][77][78], the polyad concept [79,80], and, as already suggested, stimulated the development of detection capabilities [81][82][83][84].…”

Section: Introductionmentioning

confidence: 98%

Overtone spectroscopy of molecular complexes containing small polyatomic molecules

Herman

Földes

Didriche

et al. 2016

International Reviews in Physical Chemistry

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The literature on the high-resolution spectroscopic investigation of molecular complexes containing small polyatomic species excited in their vibrational overtones is reviewed. They turn out to be complexes containing acetylene, ammonia and water, mainly excited in their 2CH, 2NH and 2OH vibrations, respectively. The majority of results published on these systems was obtained using an instrumental set-up based on cw-cavity ring-down spectroscopy, built in the 'Laboratoire de Chimie quantique et Photophysique' at the 'Université libre de Bruxelles' (CQP/ULB) and named FANTASIO+, which is described. It allowed retrieving upper state vibrational predissociation lifetimes, which are highlighted together with more results. The sequence of experiments at CQP/ULB prior and along the line of those supporting the investigation of molecular complexes is briefly illustrated.

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Molecular spectroscopy and dynamics: a polyad-based perspective

Cited by 56 publications

References 392 publications

Intuitive Understanding of σ Delocalization in Loose and σ Localization in Tight Helical Conformations of an Oligosilane Chain

Intuitive Understanding of σ Delocalization in Loose and σ Localization in Tight Helical Conformations of an Oligosilane Chain

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets

Overtone spectroscopy of molecular complexes containing small polyatomic molecules

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