Karen Louise Feilberg

The present work experimentally demonstrates that the selective excitation of the hydrogen-bonded O–H stretching fundamental (OHb) of the H2O subunit induces a concerted hydrogen-bond network rearrangement in the monoethanolamine (MEA) monohydrate embedded in neon matrices. The initially formed global potential energy minimum conformation of the MEA monohydrate adopts a cyclic cooperatively hydrogen-bonded “insertion” configuration, in which the H2O molecule simultaneously acts as a hydrogen-bond donor to the amino group and as an acceptor for the hydroxy group of MEA. The detection of this energetically favored “insertion″ conformation is based on unambiguous assignments of characteristic intramolecular vibrational transitions associated with the red-shifted O–H···O hydrogen-bonded O–H stretching motion (3507 cm–1) and the blue-shifted NH2 wagging motion (960 cm–1) of MEA together with the intermolecular large-amplitude in-plane librational (hindered overall c-type rotational) motion of H2O (452 cm–1). In addition, a strong anharmonic vibrational resonance involving the highly red-shifted O–H···N hydrogen-bonded OHb fundamental state (3262 cm–1), the HOH bending overtone state (3173 cm–1) and a ternary inter-intramolecular combination state (3348 cm–1) involving the intermolecular stretching level is rationalized by isotopic H/D and 16O/18O substitutions and is consistent with recently recognized anharmonic vibrational resonances in amine monohydrates. Upon selective infrared irradiation enabled by complementary optical filters, the excitation within this strongly resonance-coupled O–H stretching vibrational triad is shown to trigger a conformational transformation into a metastable open “addition″ configuration, which is subsequently trapped in the neon matrix cages consistent with previous findings [J. Chem. Phys., 2024, 161, 154301]. The experimental observations suggest that vibrational energy deposited in the intramolecular O–H stretching coordinate is redistributed (IVR) into one or more large-amplitude intermolecular vibrational coordinates, enabling barrier crossing on the underlying intermolecular potential energy surface prior to energy dissipation into the neon host.

Low-salinity waterflooding is widely recognized as a promising enhanced oil recovery method, yet its reported performance remains highly variable because the observed response reflects not only brine composition, but also the displacement state of the porous medium at the time the injected brine is introduced. While most previous studies have focused on optimizing brine chemistry, the mechanistic role of injection timing and displacement history has received far less attention. In this study, we investigate how the timing of brine switching governs low-salinity response in chalk by introducing an early tertiary flooding design, in which the injected brine is switched immediately after secondary brine breakthrough. This approach enables controlled probing of an intermediate saturation state representative of the reservoir region just behind the advancing flood front. The resulting recovery behavior was interpreted together with ion chromatography measurements to track brine displacement and chemical-front propagation. The results show that the apparent efficiency of low-salinity flooding is strongly governed by displacement history. Conventional tertiary injection produced negligible incremental recovery, whereas early tertiary injection of diluted seawater yielded 11.3% additional oil recovery (11.8% when formation water was used as the tertiary brine), comparable to values commonly reported for secondary low-salinity flooding. Ion chromatography revealed that the onset of tertiary oil production occurred only after the preceding brine had been displaced from the core. This indicates that chemical-front propagation, in situ mixing, and fluid accessibility govern when the tertiary response becomes observable. The data also confirmed transient formation-water banks ahead of the injected brine front. These findings indicate that tertiary low-salinity performance is controlled not only by brine composition, but also by the fluid occupancy and chemical accessibility inherited from prior flooding at the moment of brine introduction. More broadly, the results support viewing secondary, early tertiary, and conventional tertiary flooding as successive stages of flood maturity, each probing a different displacement state of the reservoir. Conventional tertiary corefloods may therefore underestimate the observable low-salinity response by introducing the modified brine only after extensive prior brine invasion and oil displacement. This highlights injection timing as a key mechanistic variable in chalk waterflooding.

A combined mid-IR and Raman jet investigation of strongly hydrogen-bonded monohydrates of tertiary amines [Lwin et al., Phys. Chem. Chem. Phys. 27, 5808–5820 (2025)] recently reported strong anharmonic vibrational resonances. These resonances involve the spectrally redshifted and strongly IR-active hydrogen-bonded O–H stretching fundamental (OHb) of H2O and several overtone and combination states involving quanta of both intramolecular and intermolecular modes, blurring the suitability of the conventional OHb fundamentals as reliable empirical indicators of the intermolecular hydrogen bond strengths. It is shown that these universal anharmonic vibrational resonances are also observed for hydrogen-bonded monohydrates of both primary and secondary amines. The present work demonstrates that isolated vibrational transitions associated with large-amplitude intermolecular out-of-plane H2O librational motion prove to be alternative robust resonance-free far-IR spectroscopic observables that correlate strongly with intermolecular hydrogen bond strength across an extended series of ether and amine monohydrates. The observed H2O librational spectral signatures are compared with a comprehensive local energy decomposition analysis of the total interaction energies predicted at the DLPNO-CCSD(T)/aug-cc-pV5Z level. The combined results show that the librational transition energies are strongly correlated with the total non-dispersive energy contributions to the directional local hydrogen bond interactions across both classes of monohydrates and to a lesser extent correlated with the additional non-directional, long-range London dispersion forces introduced by bulky alkyl substituents.

The hydrogen-bond rearrangements involved in the self-association and microhydration of the simplest vicinal diol, ethylene glycol (EG), have been explored by low-temperature mid- and far-IR cluster spectroscopy in doped neon “quantum” matrices at 4 K complemented by high-level quantum chemical conformational sampling. In addition to the reproduction of previous mid-IR jet assignments of the highly concerted hydrogen-bonded O–H stretching transitions, new distinct far-IR observations have been unambiguously attributed to transitions associated with concerted and highly anharmonic large-amplitude hindered OH (OD) torsional motion of (EG)2 and (EG-d2)2, respectively. These observations confirm the formation of a highly S4 symmetric global intermolecular potential energy minimum in the cryogenic neon environment associated with a very compact intermolecular hydrogen-bonded cyclic structure. In this conformation of (EG)2, the two intramolecular hydrogen bonds are rearranged into four new identical strongly cooperative intermolecular hydrogen bonds upon complexation as previously observed in supersonic jets. By means of selective complexation between EG and isotopically enriched H218O and D2O samples, the IR-active intramolecular hydrogen-bonded O–H stretching transitions furthermore are assigned unambiguously for the EG monohydrate. These spectroscopic observations reveal a cyclic cooperatively hydrogen-bonded structure, where the monomeric intramolecular hydrogen bond of EG is disrupted upon microhydration. In this detected conformation of the EG monohydrate, one hydroxy group acts as an intermolecular hydrogen bond donor to the H2O subunit and the vicinal hydroxy group as an intermolecular hydrogen bond acceptor to the H2O subunit in the cryogenic neon environment. The experimental findings are supported by quantum chemical analysis of the conformational potential energy landscape at the CCSD(T)-F12/cc-pVQZ-F12 level.

A recent broadband rotational spectroscopic investigation of the cross-association mechanisms of CO₂ with monoethanolamine (MEA) in molecular beams [F. Xie et al., Angew. Chem. Int. Ed., 2023, 62, e202218539] revealed an intriguing affinity of CO₂ to the hydroxy group. These findings have triggered the present systematic vibrational spectroscopic exploration of weakly bound amine··CO₂ and alcohol··CO₂ van der Waals cluster molecules embedded in inert “quantum” matrices of neon at 4.2 K complemented by high-level quantum chemical conformational analyses. The non-covalent interactions formed between the amino and hydroxy groups and the electron-deficient carbon atom of CO₂ are demonstrated to lift the degeneracy of the doubly degenerate intramolecular CO₂-bending fundamental significantly with characteristic observed spectral splittings for the amine··CO₂ (≈35–45 cm⁻¹) and alcohol··CO₂ (≈20–25 cm⁻¹) interactions, respectively, despite the almost identically predicted total association energies (≈12–14 kJ·mol⁻¹) for these van der Waals contacts, as revealed by benchmark Domain-based Local Pair Natural Orbital Coupled Cluster DLPNO-CCSD(T) theory. These high-level theoretical predictions reveal significantly higher “geometry preparation energies” for the amine··CO₂ systems leading to a more severe distortion of the CO₂ linearity upon complexation in agreement with the infrared spectroscopic findings. The systematic combined spectroscopic and quantum chemical evidences for cross-association between CO₂ and amines/alcohols in the present work unambiguously confirm an intriguing binding preference of CO₂ to the hydroxy group of the important carbon capture agent MEA, with an accurate vibrational zero-point energy corrected association energy (D₀) of 13.5 kJ·mol⁻¹ at the benchmark DLPNO-CCSD(T)/aug-cc-pV5Z level of theory.

The strong tendency for self-aggregation together with an intriguing mechanism for the microhydration of monoethanolamine (MEA) have been explored by low-temperature far-infrared cluster spectroscopy in doped neon “quantum” matrices at 4 K complemented by high-level quantum chemical modeling. In addition to the assignment of new mid-infrared perturbed intramolecular transitions, a distinct far-infrared transition is unambiguously assigned to the concerted large-amplitude hydrogen bond librational motion of the MEA homodimer. This observation confirms a global “head-to-head” intermolecular potential energy minimum associated with the formation of a compact doubly intermolecular OH⋯N hydrogen-bonded cyclic structure, where both monomeric intramolecular OH⋯N hydrogen bonds are broken upon complexation. By means of relative mixing ratio dependencies, dedicated annealing procedures, and selective complexation between MEA and isotopic H216O and H218O samples, distinct far-infrared transitions associated with large-amplitude intra-molecular hindered OH torsional motion and inter-molecular H2O librational (hindered c-type overall rotational) motion of the MEA monohydrate are furthermore assigned unambiguously for the first time. These spectroscopic observations reveal an intriguing metastable conformation, where H2O acts as a OH⋯O hydrogen bond donor to the hydroxy group instead of the amino group of MEA upon microhydration in the cryogenic neon environment, where the microhydration strengthens the intramolecular OH⋯N hydrogen bond of MEA due to hydrogen bond cooperativity.

Carboxylic acids are a small but essential compound class within petroleum chemistry, influencing crude oil behaviors in production and processing and causing environmental impacts. Detailed structural information is fundamental to understanding their influence on petroleum characteristics. However, characterizing acids in crude oil remains challenging due to matrix effects, structural diversity, and low abundance. In this work, we present a new methodology for profiling carboxylic acids by liquid-liquid extraction and selective derivatization using 4-bromo-N-methylbenzylamine (4-BNMA) followed by liquid chromatography and electrospray ionization Orbitrap mass spectrometry (LC-ESI-Orbitrap MS). The fragmentation of 4-BNMA derivatives produces a unique product ion pair, m/z 169/171, enabling the identification of chromatographic fractions containing carboxylic acids. The mass spectra of the corresponding fractions are extracted, and the acids are further computationally isolated based on the isotopic pattern. The method was optimized and validated using acid standards and systematic experimental designs, assuring robustness and sensitivity for nontarget screening purposes. This method detected up to 380 carboxylic acids in six Danish North Sea crude oils, with up to two carboxyl and other heteroatom functionalities (NSO). The results indicated that the most populated species are fatty acids (double bond equivalent (DBE) = 1) and small aromatic acids (DBE = 2-6). The predominance and diversities of compound classes in different samples are consistent with their corresponding bulk properties. Polyfunctional acids (O_x, N_xO_x, and S_xO_x) were observed due to exposure to oxidation and biodegradation. Also, the approach's applicability benefits high-resolution MS analysis by simplifying data processing for crude oil and potentially other high-organic and aqueous samples.