The weak fundamental NH-stretching transition in amines

Schrøder, Sidsel D.; Hansen, Anne S.; Wallberg, Jens; Nielsen, Anne R.; Du, Lin; Kjaergaard, Henrik G.

doi:10.1016/j.saa.2016.09.003

Cited by 7 publications

(5 citation statements)

References 32 publications

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“…Kjaergaard and coauthors showed that changes of dipole moment functions in a set of seven NH-containing molecules have a considerable range of variation, and hence, intensities of νNH and 2νNH transitions vary a lot. 62 For gaseous pyrrole, the intensity drop of about 8 from νNH to 2νNH 60 is similar to that reported for a relative change in intensities of νOH and 2νOH bands, which drop by a factor of about 10 in the gas phase. 5 In this respect, it appears interesting to us to report that for matrix-isolated 5MOI the experimental integrated intensities of νNH and 2νNH differ by a factor of 34 (see Figure 4).…”

Section: Resultssupporting

confidence: 83%

“…Fewer studies have been done on N–H transitions. Kjaergaard and coauthors showed that changes of dipole moment functions in a set of seven NH-containing molecules have a considerable range of variation, and hence, intensities of νNH and 2νNH transitions vary a lot . For gaseous pyrrole, the intensity drop of about 8 from νNH to 2νNH is similar to that reported for a relative change in intensities of νOH and 2νOH bands, which drop by a factor of about 10 in the gas phase .…”

Section: Results and Discussionsupporting

confidence: 58%

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Conformational Changes in 5-Methoxyindole: Effects of Thermal, Vibrational, and Electronic Excitations

2017

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The molecule of 5-methoxyindole (5MOI) may adopt two conformational states, syn and anti, with respect to the relative orientation of the NH and OCH groups. The structure of monomeric 5MOI was characterized spectroscopically, in mid- and near-infrared domains. The conformational composition of 5MOI could be controlled in three different ways. Thermally, two conformers of 5MOI could be trapped in xenon matrixes at 16 K. Upon annealing the xenon matrix to temperatures about 30-40 K, the higher-energy syn form converted to the ground-state anti conformer. Vibrational excitations in the near-infrared domain, at the frequency of the first NH stretching overtone, 6853 cm, afforded the inverse conformational transformation, and a part of the anti conformer was upconverted to the syn form. Electronic excitations in the UV domain, at 315-310 nm, resulted in a total consumption of the syn form again, in favor of anti. Upon further irradiations at 308 nm, a partial repopulation of the syn form, at the expense of anti, was observed. We propose a mechanistic explanation of the observed transformations, which is based on computations of the vibrational spectra of the two conformers and also on computations of the ground state S and the first excited state S potential energy surfaces along the coordinate for conformational isomerization. The highlights of the present work are the first experimental observation of the minor syn conformer of 5MOI, evidence of the long-range vibrational energy transfer resulting in conformational isomerization upon excitation of the NH stretching overtone, and the possibility of partial conformational control of 5MOI by using electronic excitations.

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Section: Resultssupporting

confidence: 83%

Section: Results and Discussionsupporting

confidence: 58%

Conformational Changes in 5-Methoxyindole: Effects of Thermal, Vibrational, and Electronic Excitations

2017

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“…For the OH-stretching overtones, the 1D and 3D LM calculated intensities are similar and generally within 10–20% of the experimental intensities, i.e., comparable to the variation between CCSD(T)-F12a/VDZ-F12 and CCSD(T)/aug-cc-pVTZ 1D LM intensities . The similarity of the 1D and 3D LM overtone intensities, as well as the small Eckart correction, is not surprising given that the 1D LM model has previously been successful in describing overtone intensities. ,, However, the conventional use of the Morse potential to represent the 1D LM PES leads to overtone intensities that are generally underestimated compared to experiments. − For the Δ v OH = 3 transitions, the experimental intensities presented in Table are generally slightly larger than those presented in ref . For these transitions, several weak combination bands that primarily obtain their intensity from the OH-stretch are present at the higher-energy side of the bands.…”

Section: Resultssupporting

confidence: 69%

“…53 The similarity of the 1D and 3D LM overtone intensities, as well as the small Eckart correction, is not surprising given that the 1D LM model has previously been successful in describing overtone intensities. 53,69,70 However, the conventional use of the Morse potential to represent the 1D LM PES leads to overtone intensities that are generally underestimated compared to experiments. 71−74 For the Δv OH = 3 transitions, the experimental intensities presented in Table 2 are generally slightly larger than those presented in ref 54.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Accurate Calculations of OH-Stretching Intensities with a Reduced-Dimensional Local Mode Model Including Eckart Axis Embedding

2020

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Absolute OH-and OD-stretching transition intensities have been calculated for a series of alcohols (methanol, ethanol, 2-propanol, 1-propanol, and tert-butanol) with onedimensional (1D) and three-dimensional (3D) local mode models. We compare the calculated intensities for the Δv OH = 1−5 and Δv OD = 1−3 transitions with experimental values. Potential energy and dipole moment surfaces are calculated at the CCSD(T)-F12a/ VDZ-F12 level of theory. The 1D local mode model includes only the OH(D)-stretching mode, whereas the 3D local mode model also includes the CO-stretching and COH(D)-bending modes. We analyze the effect on vibrational intensities of using either a molecule-fixed Eckart frame or a space-fixed Cartesian frame. We find that both Eckart embedding and inclusion of the COstretching and COH(D)-bending modes in the local mode model are important for the OH/OD-stretching fundamental transition intensities, but have a minor effect on overtone intensities. The 3D reduced-dimensional local model, when combined with coupled cluster surfaces, accurately predicts OH/OD-stretching transition intensities and wavenumbers, for all alcohols included in this work.

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“…Noticeably, the anharmonic frequency computations predict the IR intensities of the 2n(NH) first stretching overtone modes to be equal to or even higher than those corresponding to the n(NH) stretching fundamental modes (Tables 2-5). This interesting phenomenon has been reported by Kjaergaard et al for primary and secondary amines, [100][101][102] however, to the best of our knowledge, no molecules with imino groups have been reported exhibiting the same peculiarity so far.…”

Section: Selective Sh Rotamerization Induced By Near-ir Irradiationsupporting

confidence: 73%

Selective conformational control by excitation of NH imino vibrational antennas

Góbi

Reva

Csonka

et al. 2019

Phys. Chem. Chem. Phys.

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The weak fundamental NH-stretching transition in amines

Cited by 7 publications

References 32 publications

Conformational Changes in 5-Methoxyindole: Effects of Thermal, Vibrational, and Electronic Excitations

Conformational Changes in 5-Methoxyindole: Effects of Thermal, Vibrational, and Electronic Excitations

Accurate Calculations of OH-Stretching Intensities with a Reduced-Dimensional Local Mode Model Including Eckart Axis Embedding

Selective conformational control by excitation of NH imino vibrational antennas

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