Argon Matrix Research Articles

Infrared Spectroscopy and Photochemistry of Anthracoronene in Cosmic Water Ice.

We present a laboratory study of the polycyclic aromatic hydrocarbon (PAH) anthracoronene (AntCor, C36H18) in simulated interstellar ices in order to determine its possible contribution to the broad infrared absorption bands in the 5–8 μm wavelength interval. The Fourier transform infrared (FTIR) spectrum of AntCor, codeposited with water ice, was collected. The FTIR spectrum of the sample irradiated with ultraviolet photons was also collected. Unirradiated and UV-irradiated AntCor embedded in water ice have not been studied before; therefore, the molecule’s band positions and intensities were compared to published data on AntCor in an argon matrix and theoretical calculations (DFT), as well as the published results of its parent molecules, coronene and anthracene, in water ice. The experimental band strengths for unirradiated AntCor exhibit variability as a function of PAH:H2O concentration, with two distinct groupings of band intensities. AntCor clustering occurs for all concentrations and has a significant effect on PAH degradation rates and photoproduct variability. Near-IR spectra of irradiated AntCor samples show that AntCor+ production increases as the concentration of AntCor in water ice decreases. Photoproduct bands are assigned to AntCor+, cationic alcohols, protonated AntCor, and ketones. We report the rate constants of the photoproduct production for the 1:1280 AntCor:H2O concentration. CO2 production from AntCor is much less than what was previously reported for Ant and Cor and exhibits two distinct regimes as a function of AntCor:H2O concentration. The contribution of AntCor photoproducts to astronomical spectra can be estimated by comparison with the observed intensities in the 7.4–8.0 μm range.

Modeling the heating and cooling of a chromophore after photoexcitation.

The heating of a chromophore due to internal conversion and its cooling down due to energy dissipation to the solvent are crucial phenomena to characterize molecular photoprocesses. In this work, we simulated the ab initio nonadiabatic dynamics of cytosine, a prototypical chromophore undergoing ultrafast internal conversion, in three solvents—argon matrix, benzene, and water—spanning an extensive range of interactions. We implemented an analytical energy-transfer model to analyze these data and extract heating and cooling times. The model accounts for nonadiabatic effects, and excited- and ground-state energy transfer, and can analyze data from any dataset containing kinetic energy as a function of time. Cytosine heats up in the subpicosecond scale and cools down within 25, 4, and 1.3 ps in argon, benzene, and water, respectively. The time constants reveal that a significant fraction of the benzene and water heating occurs while cytosine is still electronically excited.

Raman study of water deposited in solid argon matrix

New Raman data are presented concerning H2O and D2O water aggregation in argon matrix having the ratio of number of argon atoms to water molecules close to 40:1. Experiments were conducted at temperatures from 8 K to 34 K allowing observation of OH and OD stretching vibrations of water monomers, dimers, trimers and higher multimers, as well as broad bands corresponding to solid amorphous water. Molecular dynamics simulations were performed for thirteen or sometimes fourteen water molecules dispersed among 500 argon atoms. Resulting final configurations included dimers, trimers, tetramers and pentamers, all in open chain configurations which upon optimization resulted in mostly cyclic conformations. Observed OH stretching vibrations were assigned by comparing calculated normal modes in harmonic approximation at the B3LYP/aug-cc-pVDZ and PBEPBE1/aug-cc-pVDZ level of theory with our data and previously observed bands from infrared matrix isolation studies and Raman jet cooled experiments. Raman bands assigned to water multimers in argon matrix are shifted 20 to 25 cm−1 towards lower wavenumbers with respect to the positions of OH stretching vibrations of almost free water clusters.

(Noble Gas)n -NC+ Molecular Ions in Noble Gas Matrices: Matrix Infrared Spectra and Electronic Structure Calculations.

An investigation of pulsed‐laser‐ablated Zn, Cd and Hg metal atom reactions with HCN under excess argon during co‐deposition with laser‐ablated Hg atoms from a dental amalgam target also provided Hg emissions capable of photoionization of the CN photo‐dissociation product. A new band at 1933.4 cm−1 in the region of the CN and CN+ gas‐phase fundamental absorptions that appeared upon annealing the matrix to 20 K after sample deposition, and disappeared upon UV photolysis is assigned to (Ar) n CN+, our key finding. It is not possible to determine the n coefficient exactly, but structure calculations suggest that one, two, three or four argon atoms can solvate the CN+ cation in an argon matrix with C−N absorptions calculated (B3LYP) to be between 2317.2 and 2319.8 cm−1. Similar bands were observed in solid krypton at 1920.5, in solid xenon at 1935.4 and in solid neon at 1947.8 cm−1. H13CN reagent gave an 1892.3 absorption with shift instead, and a 12/13 isotopic frequency ratio–nearly the same as found for 13CN+ itself in the gas phase and in the argon matrix. The CN+ molecular ion serves as a useful infrared probe to examine Ng clusters. The following ion reactions are believed to occur here: the first step upon sample deposition is assisted by a focused pulsed YAG laser, and the second step occurs on sample annealing: (Ar)2 ++CN→Ar+CN+→(Ar) n CN+.

Spectroscopy and radiation-induced chemistry of an atmospherically relevant CH2F2…H2O complex: Evidence for the formation of CF2…H2O complex as revealed by FTIR matrix isolation and ab initio study

Difluoromethane is considered among the environment friendly alternatives to the ozone depleting chlorofluorocarbons. Due to its chemical inertness and lack of UV absorption above 200 nm, this compound can easily come to the upper layers forming complexes with widely abundant atmospheric components, such as water. The radiation-induced degradation of this compound and its complexes may be significant for reliable prediction of its long-term evolution in the environment as well as for development of new ways for its removal. In this work we have studied the vibrational spectroscopic properties and mechanisms of the radiation-induced decay of the CH2F2⋯H2O under the action of X-rays using matrix isolation FTIR spectroscopy and ab initio calculations. The IR spectrum of the complex in an argon matrix was characterized for the first time and assigned to a hydrogen-bonded structure with a binding energy of 11.1 kJ/mol (2.65 kcal/mol) (CCSD(T)/CBS level of theory). Complexation with water leads to a certain suppression of the efficiency of the radiation-induced decomposition of difluoromethane. The obtained results provide evidence for the radiation-induced formation of previously unreported CF2⋯H2O complex (in addition to other oxygen containing molecules, such as COF2 and CO). As demonstrated by calculations, the new difluorocarbene complex reveals a hydrogen bond and it is characterized by a binding energy of 5.73 kJ/mol (1.37 kcal/mol) (CCSD(T)/CBS level of theory).

IR spectroscopic study of the dichloromethyl peroxyl radical and its deuterated analogs in the argon matrix

IR spectroscopic study of the dichloromethyl peroxyl radical and its deuterated analogs in the argon matrix

Conformational Space, IR-Induced, and UV-Induced Chemistry of Carvacrol Isolated in a Low-Temperature Argon Matrix.

In this work, monomers of carvacrol (5-isopropyl-2-methylphenol), a natural monoterpene exhibiting wide range bioactivity, were trapped in a cryogenic argon matrix and characterized by infrared spectroscopy, while quantum chemical calculations at the B3LYP and MP2 levels were employed to characterize the conformational landscape of the isolated molecule. Four conformers have been localized on the potential energy surface, and the factors accounting for their relative stability were analyzed. The two most stable conformers of carvacrol, differing in the relative orientation of the isopropyl group and both having the OH group pointing away from the vicinal methyl fragment, were identified in the cryomatrix for the first time. The individual spectral signatures of the two conformers were distinguished based on the change in their relative abundance induced by exposing the matrix to broadband infrared light. Matrix-isolated carvacrol was also irradiated with broadband UV light (λ > 200 nm), which resulted in the cleavage of the OH group. Recombination of the released H atom at the ortho- or para-position of the ring resulted in the formation of alkyl-substituted cyclohexadienones. These were found to undergo subsequent valence and open-ring isomerizations, leading, respectively, to the formation of a Dewar isomer and open-chain conjugated ketenes. Decarbonylation of the photoproducts was also observed for longer irradiation times. A mechanistic analysis of the observed photochemical transformations is presented.

Photolysis of 3-Azido-3-phenyl-3H-isobenzofuran-1-one at Ambient and Cryogenic Temperatures.

Although alkyl azides are known to typically form imines under direct irradiation, the product formation mechanism remains ambiguous as some alkyl azides also yield the corresponding tripletalkylnitrenes at cryogenic temperatures. The photoreactivity of 3-azido-3-phenyl-3H-isobenzofuran-1-one (1) was investigated in solution and in cryogenic matrices. Irradiation (λ = 254 nm) of azide 1 in acetonitrile yielded a mixture of imines 2 and 3. Monitoring of the reaction progress using UV-Vis absorption spectroscopy revealed an isosbestic point at 210 nm, indicating that the reaction proceeded cleanly. Similar results were observed for the photoreactivity of azide 1 in a frozen 2-methyltetrahydrofuran (mTHF) matrix. Irradiation of azide 1 in an argon matrix at 6 K resulted in the disappearance of its IR bands with the concurrent appearance of IR bands corresponding to imines 2 and 3. Thus, it was theorized that azide 1 forms imines 2 and 3 via a concerted mechanism from its singlet excited state or through singletalkylnitrene 1 1N, which does not intersystem cross to its triplet configuration. This proposal was supported by CASPT2 calculations on a model system, which suggested that the energy gap between the singlet and triplet configurations of alkylnitrene 1N is 33 kcal/mol, thus making intersystem crossing inefficient.

Molecular structure, spectroscopy and photochemistry of alprazolam

In this article, a comprehensive study of the molecular structure, spectroscopy, and photochemistry of alprazolam (Xanax®; 8-chloro-1-methyl-6-phenyl-4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepine) is reported. The structure of the isolated molecule of the compound was investigated using density functional theory (DFT), revealing that the molecule exists in a single conformer, which is associated with 12 equivalent-by-symmetry minima. The molecules of the compound were trapped from the gas phase into a low temperature (10 K) argon matrix, and the infrared (IR) spectrum of the matrix-isolated monomers was obtained and assigned. The matrix-isolated molecules were then subjected to in situ ultraviolet (UV) irradiation. It was concluded that alprazolam is photostable under these experimental conditions, contrarily to what is known to happen for the compound in solution or in solid state in the presence of excipients used in the pharmaceutical formulations. An explanation for the photostability of the matrix-isolated compound is provided, based on rapid recombinations of the biradical formed from the UV-induced diazepine ring cleavage or the chlorine atom and the complementary radical resulting from the scissoring of the C–Cl bond, which are favored by the cage confinement of the matrix-isolated molecules. The major fragmentation channels of the alprazolam molecule upon electron bombardment (70 eV) were determined by analysis of its electron ionization mass spectrum, which reveals that the major primary fragmentation processes lead to formation of cyanobenzene, N2, HCl (Cl2), and benzene.The compound was also investigated in solution by multinuclear (1H, 13C and 15N) nuclear magnetic resonance (NMR) and ultraviolet (UV) spectroscopies, and in crystalline phase (P-1 polymorph) through IR and Raman spectroscopies. In addition, the structure of the crystal, previously reported in the literature [M. R. Caira, B. Easter, S. Honiball, A. Horne and L. R. Nassimbeni, Structure and Thermal Stability of Alprazolam and Selected Solvates, J. Pharm. Sci., 1995, 84, 1379–1384], was revisited in order to evaluate the relative importance of the different types of intermolecular interactions, using Hirshfeld surface analysis, the CE-B3LYP energy decomposition model, and the harmonic oscillator model of aromaticity (HOMA) index. Finally, the enthalpy of sublimation of the crystal was estimated from the CE-B3LYP calculated lattice energy.

Cyanides, Isocyanides, and Hydrides of Zn, Cd and Hg from Metal Atom and HCN Reactions: Matrix Infrared Spectra and Electronic Structure Calculations.

Zinc and cadmium atoms from laser ablation of the metals and mercury atoms ablated from a dental amalgam target react with HCN in excess argon during deposition at 5 K to form the MCN and MNC molecules and CN radicals. UV irradiation decreases the higher energy ZnNC isomer in favor of the lower energy ZnCN product. Cadmium and mercury atoms produce analogous MCN primary molecules. Laser ablation of metals also produces plume radiation which initiates H‐atom detachment from HCN. The freed H atom can add to CN radical to produce the HNC isomer. The argon matrix also traps the higher energy but more intensely absorbing isocyanide molecules. Further reactions with H atoms generate HMCN and HMNC hydrides, which can be observed by virtue of their C−N stretches and intense M−H stretches. Computational modeling of IR spectra and relative energies guides the identification of reaction products by providing generally reliable frequency differences within the Zn, Cd and Hg family of products, and estimating isotopic shifts using to 13C and 15N isotopic substitution for comparison with experimental data.

Structure and IR Spectra of 3(5)-Aminopyrazoles and UV-Induced Tautomerization in Argon Matrix.

The prototropic tautomerism in 3(5)-aminopyrazoles was investigated by matrix isolation infrared (IR) spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. In consonance with the experimental data, the calculations predict tautomer 3-aminopyrazole (3AP) to be more stable than the 5-aminopyrazole (5AP) tautomer (calculated energy difference: 10.7 kJ mol−1; Gibbs free energy difference: 9.8 kJ mol−1). The obtained matrix isolation IR spectra (in both argon and xenon matrices) were interpreted, and the observed bands were assigned to the tautomeric forms with help of vibrational calculations carried out at both harmonic and anharmonic levels. The matrix-isolated compound (in argon matrix) was then subjected to in situ broadband UV irradiation (λ > 235 nm), and the UV-induced transformations were followed by IR spectroscopy. Phototautomerization of the 3AP tautomer into the 5AP form was observed as the strongly prevalent reaction.

Matrix Isolation-Vibrational Circular Dichroism Spectroscopic Study of Conformations and Non-Covalent Interactions of Tetrahydro-2-Furoic Acid.

The conformational landscape and aggregation behaviour of tetrahydro-2-furoic acid (THFA) were investigated by using matrix isolation-vibrational circular dichroism (MI-VCD). The well-resolved experimental MI-IR and MI-VCD features in an argon matrix at 10 K allow one to identify two dominant monomeric conformations as trans-THFA where the hydroxyl and carbonyl groups of COOH are at opposite sides, as well as one cis-conformer. At 24 K and 30 K deposition temperatures, the experimental IR and VCD spectral features reveal further growth of the binary THFA aggregates. Systematic conformational searches identified three vastly different binary binding topologies, resulting in a few hundred stable (THFA)2 conformers. Interestingly, the main binary structures observed correspond to an unusual type of structure which is made of two trans-THFA subunits, in contrast to the usual double H-bonded ring binary structures, identified in a previous solution study. The present work showcases the power of MI-VCD spectroscopy in revealing unusual structures formed in a cold rare gas matrix.

Polymorphism and Conformational Equilibrium of Nitro-Acetophenone in Solid State and under Matrix Conditions.

Conformational and polymorphic states in the nitro-derivative of o-hydroxy acetophenone have been studied by experimental and theoretical methods. The potential energy curves for the rotation of the nitro group and isomerization of the hydroxyl group have been calculated by density functional theory (DFT) to estimate the barriers of the conformational changes. Two polymorphic forms of the studied compound were obtained by the slow and fast evaporation of polar and non-polar solutions, respectively. Both of the polymorphs were investigated by Infrared-Red (IR) and Raman spectroscopy, Incoherent Inelastic Neutron Scattering (IINS), X-ray diffraction, nuclear quadrupole resonance spectroscopy (NQR), differential scanning calorimetry (DSC) and density functional theory (DFT) methods. In one of the polymorphs, the existence of a phase transition was shown. The position of the nitro group and its impact on the crystal cell of the studied compound were analyzed. The conformational equilibrium determined by the reorientation of the hydroxyl group was observed under argon matrix isolation. An analysis of vibrational spectra was achieved for the interpretation of conformational equilibrium. The infrared spectra were measured in a wide temperature range to reveal the spectral bands that were the most sensitive to the phase transition and conformational equilibrium. The results showed the interrelations between intramolecular processes and macroscopic phenomena in the studied compound.

Intermediates of Carbon Monoxide Oxidation on Praseodymium Monoxide Molecules: Insights from Matrix-Isolation IR Spectroscopy and Quantum-Chemical Calculations.

Identifying reaction intermediates in gas-phase investigations will provide understanding for the related catalysts in fundamental aspects including bonding interactions of the reaction species, oxidation states (OSs) of the anchored atoms, and reaction mechanisms. Herein, carbon monoxide (CO) oxidation by praseodymium monoxide (PrO) molecules has been investigated as a model reaction in solid argon using matrix-isolation IR spectroscopy and quantum-chemical calculations. Two reaction intermediates, OPr(η1-CO) and OPr(η2-CO), have been trapped and characterized in argon matrixes. The intermediate OPr(η2-CO) shows an extremely low C-O stretching band at 1624.5 cm-1. Quantum-chemistry studies indicate that the bonding in OPr(η1-CO) is described as "donor-acceptor" interactions conforming to the Dewar-Chatt-Duncanson motif. However, the bonding in OPr(η2-CO) results evidently from a combination of dominant ionic forces and normal Lewis "acid-base" interactions. The electron density of the singly occupied bonding orbital is strongly polarized to the CO fragment in OPr(η2-CO). Electronic structure analysis suggests that the two captured species exhibit Pr(III) OSs. Besides, the pathways of CO oxidation have been discussed.

Structural Relevance of Intramolecular H-Bonding in Ortho-Hydroxyaryl Schiff Bases: The Case of 3-(5-bromo-2-hydroxybenzylideneamino) Phenol.

A new Schiff base compound, 3-(5-bromo-2-hydroxybenzylideneamino)phenol (abbreviated as BHAP) was synthesized and characterized by 1H- and 13C- nuclear magnetic resonance and infrared spectroscopies. DFT/B3LYP/6-311++G(d,p) calculations were undertaken in order to explore the conformational space of both the E- and Z- geometrical isomers of the enol-imine and keto-amine tautomers of the compound. Optimized geometries and relative energies were obtained, and it was shown that the most stable species is the E-enol-imine form, which may exist in four low-energy intramolecularly hydrogen-bonded forms (I, II, V, and VI) that are almost isoenergetic. These conformers were concluded to exist in the gas phase equilibrium with nearly equal populations. On the other hand, the infrared spectra of the compound isolated in a cryogenic argon matrix (10 K) are compatible with the presence in the matrix of only two of these conformers (conformers II and V), while conformers I and VI convert to these ones by quantum mechanical tunneling through the barrier associated with the rotation of the OH phenolic group around the C–O bond. The matrix isolation infrared spectrum was then assigned and interpreted with help of the DFT(B3LYP)/6-311++G(d,p) calculated infrared spectra for conformers II and V. In addition, natural bond orbital (NBO) analysis was performed on the most stable conformer of the experimentally relevant isomeric form (E-enol-imino conformer V) to shed light on details of its electronic structure. This investigation stresses the fundamental structural relevance of the O–H···N intramolecular H-bond in o-hydroxyaryl Schiff base compounds.

Infrared Spectra and Theoretical Calculations of BSe2 and BSe2-: The Pseudo-Jahn-Teller Effect.

Matrix isolation infrared spectroscopy has been employed to study the reaction of laser-ablated boron atoms with hydrogen selenide in a 5 K solid argon matrix. On the basis of the isotopic shifts as well as the theoretical frequency calculations, triatomic molecule BSe2 and its anion BSe2- were identified. Both BSe2 and BSe2- were predicted to have D∞h symmetric structures with nearly identical structure parameters and bond strengths by quantum chemical calculations. Whereas the observed antisymmetric B-Se stretching frequency of BSe2 is much lower than that of BSe2-, the anomalously low antisymmetric B-Se stretching frequency of BSe2 is attributed to a pseudo-Jahn-Teller effect due to the mixing of the X2Πg ground state with the A2Πu excited state. In addition, H2BSe, HBSe, and HSeBSe molecules were produced in the reaction.

UV-Induced Photochemistry of 1,3-Benzoxazole, 2-Isocyanophenol, and 2-Cyanophenol Isolated in Low-Temperature Ar Matrixes.

The monomers of 1,3-benzoxazole isolated in a cryogenic argon matrix were characterized by infrared spectroscopy. The photochemistry of matrix-isolated 1,3-benzoxazole, induced by excitation with a frequency-tunable narrowband UV light, was investigated. Irradiation at 233 nm resulted in a nearly quantitative conversion of 1,3-benzoxazole into 2-isocyanophenol. The individual photochemical behavior of the in situ produced 2-isocyanophenol was studied upon excitations at 290 nm, where 1,3-benzoxazole does not react. The photochemistry of isomeric matrix-isolated 2-cyanophenol was also studied. The photoreactions of 2-substituted (cyano- or isocyano-) phenols were found to have many similarities: (i) OH bond cleavage, yielding a 2-substituted (cyano- or isocyano-) phenoxyl radical and an H-atom, (ii) recombination of the detached H-atom, resulting in an oxo tautomer, and (iii) decomposition leading to fulvenone, together with HCN and HNC. In another photoprocess, 2-cyanophenol undergoes a [1,5] H-shift from the hydroxyl group to the cyano group yielding isomeric ketenimine. The analogous [1,5] H-shift from the hydroxyl group to the isocyano group must have also occurred in 2-isocyanophenol; however, the resulting nitrile ylide isomer is kinetically unstable and collapses to benzoxazole. All photoproducts were characterized by comparing their observed infrared spectra with those computed at the B3LYP/6-311++G(d,p) level. The mechanistic analysis of the photochemistry occurring in the family of the title compounds is presented.

A comparison of the wavelength-dependent photochemical reactions of ozone with vinyl bromide and fluoride in argon matrices

A study of the photolytically-induced reactions of ozone with vinyl bromide and vinyl fluoride, H2CCHX (X = F, Br), in argon matrixes is described, after either red LED (625 nm) or Hg pen lamp (254 nm) irradiation. Products were observed using infrared spectroscopy and identification was aided by 18O labeling experiments. The experimental work was supported by extensive DFT calculations. For vinyl bromide, bromoacetaldehyde was the dominant product despite the fact that acetyl bromide was calculated to be the most energetically favored product. Lesser amounts of bromooxirane and possibly bromovinyl alcohol were observed. These results are in agreement with an earlier study of the photochemical reaction of ozone with vinyl chloride. In contrast, the overall product yield with vinyl fluoride was much lower. Fluorooxirane was the main product with only a hint of fluoroacetaldehyde despite that fact that fluorooxirane was calculated to be higher in energy than either acetyl fluoride or fluoroacetaldehyde.

Conformational composition of 1-butanol in matrix isolation

IR absorption spectra of 1-butanol isolated in an argon matrix were obtained at temperatures from 10 to 50 K. The conformational behavior of 1-butanol was analyzed using the results of quantum-chemical simulation of the structure and vibrational spectra of its small clusters. We studied the conformational composition of 1-butanol in matrix isolation and showed the transformation of its structure that occurs with an increase in the matrix temperature.

Confinement effects on C–H and C–F stretching vibrational frequencies of difluoromethane in cold inert gas matrixes: a combined infrared spectroscopy and electronic structure theory study

Mid-infrared spectra of difluoromethane (DFM) have been recorded by confining the molecule in the matrix cages of pure argon, nitrogen and in the mixed matrixes of argon and nitrogen obtained by mixing the two gases in definite proportions. The measured spectra depict distinct confinement effects in terms of the infrared spectral shifts of the C–H and C–F stretching vibrational fundamentals as compared to the free molecules in the gas-phase, and also some remarkable changes in band appearances and relative intensities. The signs of the spectral shifts are observed to be different for the $$\upnu _{\text {C--H}}$$ and $$\upnu _{\text {C--F}}$$ transitions. Pronounced blue shifts are observed for the two $$\upnu _{\text {C--H}}$$ modes in pure nitrogen matrix, which progressively reduce in magnitude in the mixed matrixes, and is least in the pure argon matrix. On the other hand, distinct red shifts of the $$\upnu _{\text {C--F}}$$ vibrations are evident in pure nitrogen matrix, which are reduced in magnitude in the mixed matrixes, and become even less pronounced in pure argon matrix. The effect of Fermi resonances in the $$\upnu _{\text {C--H}}$$ region, that has motivated several previous investigations of DFM including high resolution gas phase studies, becomes explicit upon comparison of the matrix isolation spectrum with the gas phase spectrum. Electronic structure calculations using several DFT and DFT-D methods, in conjunction with NBO analysis, have been carried out for various sizes of $$\hbox {DFM-N}_{2}$$ and DFM-Ar complexes in order to understand the underlying interactions responsible for the observed shifts. The calculations are found to satisfactorily reproduce the observed variations in magnitude and direction of the shifts of both the $$\upnu _{\text {C--H}}$$ and $$\upnu _{\text {C--F}}$$ transitions for the change of the medium. It is inferred that the inert gas matrix environment exerts an electronic re-organization within the DFM molecule, and the consequent rehybridization of the carbon-centric hybrid orbital of the C–H and C–F bonds is responsible for the observed spectral shifts.