Binding energies and dissociation pathways in the aniline-Ar2 cation complex

Fragmentation route of doubly ionized benzene, aniline, and nitroanilines monomers using a novel protocol from density functional theory and QTAIM

The possibility of finding the fragmentation routes by theoretical methods led us to compare the molecular ions between neutral molecules of benzene, aniline, and o-, m-, and p-nitroaniline, using the density functional theory (DFT), under an aug-cc-pVDZ base set and a B3LYP exchange-correlation functional. After determining the structure and electronic energy of neutral and doubly ionized species, we used a new protocol based on analyzing Wiberg's binding indexes and the quantum theory of atoms in Bader molecules (QTAIM). The charge transfer and electronic distribution in aromatic monomers indicate the possibility of fragment formation in at least two pairs of carbon-carbon (CC) atoms. They show the possible loss of the -CNH₂ and -NO₂ groups in the aniline and nitroaniline molecules doubly ionized.

Ionization spectroscopies and theoretical calculations of cis and trans 3-fluoro-N-methylaniline-Arn(n=1,2) van der Waals clusters: Structures and binding energies

The ab initio and dispersion-corrected density functional theory (DFT) calculations of the van der Waals (vdW) clusters of cis and trans 3-fluoro-N-methylaniline-Ar_n (3FNMA-Ar_n) (n=1,2) predict that, for cis and trans 3FNMA-Ar₁ clusters, the π-bound geometry with the Ar atom sitting over the ring is the global minimum in both neutral and cationic states, while for cis and trans 3FNMA-Ar₂ clusters, the [π|π]-bound sandwich structure with two Ar ligands occupying nearly equivalent π-bound positions above and below the ring plane is the global minimum. The vibronic spectra of cis and trans 3FNMA-Ar₁ clusters in the S₁ state were recorded by using one-color and two-color resonant two-photon ionization (R2PI) techniques, the comparison of which yields an estimate of the binding energy of cluster in the S₁ state. It is found that the linear correlation between the redshift of the S₁←S₀ electronic transition energy (E₁) of cluster and the E₁ of the monomer also holds for the Ar clusters of hetero-di-substituted aromatics. By recording the photoionization efficiency (PIE) curves and mass-analyzed threshold ionization (MATI) dissociation spectra of cis and trans 3FNMA-Ar₁ clusters, the ionization energies (IE) and binding energies of clusters in the D₀ state are obtained. The MATI spectra of the cis and trans 3FNMA-Ar₁ cations exhibit significant progressions of the vdW bending mode (b_x), indicating the structural changes of the clusters in the bending coordinate upon ionization. The combination of the three kinds of spectroscopic methods provides the binding energies of cis and trans 3FNMA-Ar₁ clusters in the S₀, S₁ and D₀ states with good accuracy, and the values estimated by dispersion-corrected DFT calculations compare well with the experimental results. From our studies, the ωB97X-D and TD-ωB97X-D methods using high quality basis set are recommended for studying the intermolecular interaction of such vdW clusters in the ground and excited states.

Quantitative probing of subtle interactions among H-bonds in alpha hydroxy carboxylic acid complexes

The alpha OH stretching frequency may be affected upon complexing with water and formic acid.

Influences of the propyl group on the van der Waals structures of 4-propylaniline complexes with one and two argon atoms studied by electronic and cationic spectroscopy

4-propylaniline complexes with one and two argon atoms formed in the molecular beam were studied in the first excited electronic state, S1, using resonance enhanced two-photon ionization spectroscopy and in the cation ground state, D0, using mass analyzed threshold ionization spectroscopy. The combination of electronic and cationic spectra of the clusters allows two conformations to be identified in both aniline-Ar1 and aniline-Ar2, which are assigned to either the gauche configuration or anti-configuration of 4-propylaniline. The gauche isomer exhibits complex bands shifted 29 cm(-1) and 89 cm(-1) from the S1 origin bands and 83 cm(-1) and 148 cm(-1) from the ionization potential assigned to the Ar1 and Ar2 complexes, respectively. For the anti-rotamer, the corresponding shifts actually become nearly additive, 53 cm(-1) and 109 cm(-1) for the S1 origin bands, and 61 cm(-1) and 125 cm(-1) for the ionization potentials. Ab initio calculations provide insights into the influences of the propyl and amino groups on the positions of the argon atoms within the clusters. In addition, the binding energy of one argon with the gauche isomer of 4-propylaniline has been measured to be 550 ± 5 cm(-1) in the D0 state, 496 ± 5 cm(-1) in the S1 state, and 467 ± 5 cm(-1) in the neutral ground state, S0.

Structure and energetics of the anisole–Arn (n = 1, 2, 3) complexes: high-resolution resonant two-photon and threshold ionization experiments, and quantum chemical calculations

We present a concerted experimental and theoretical study of the anisole⋯Ar_n complexes with n = 1–3.

Communication: The ionization spectroscopy of mixed carboxylic acid dimers

We report mass analyzed threshold ionization spectroscopy of supersonically cooled gas phase carboxylic complexes with 9-hydroxy-9-fluorenecarboxylic acid (9HFCA), an analog of glycolic acid. The vibrationally resolved cation spectrum for the 9HFCA complex with formic acid allows accurate determination of its ionization potential (IP), 64,374 ± 8 cm(-1). This is 545 cm(-1) smaller than the IP of 9HFCA monomer. The IPs of 9HFCA complexes with acetic acid and benzoic acid shift by -1133 cm(-1) and -1438 cm(-1), respectively. Density functional calculations confirm that Cs symmetry is maintained upon ionization of the 9HFCA monomer and its acid complexes, in contrast to the drastic geometric rearrangement attending ionization in complexes of 9-fluorene carboxylic acid. We suggest that the marginal geometry changes and small IP shifts are primarily due to the collective interactions among one intramolecular and two intermolecular hydrogen bonds in the dimer.

Theoretical and REMPI spectroscopic study on phenylhydrazine and phenylhydrazine-(Ar)n (n=1, 2) van der Waals complexes

Phenylhydrazine and its van der Waals complexes with one or two argon atoms were investigated with theoretical calculations and resonant two photon ionization (R2PI) spectroscopy. The ab initio and DFT calculations found a conversion of the orbital hybridization of the Nbeta atom from sp3-like in the S0 state to sp2-like in the S1 state, suggesting that the lone pair electrons of the Nbeta atom are involved in a super p-p-pi conjugation over the skeleton of phenylhydrazine in the S1 state. The structural change of the hydrazino group in the S1<--S0 electronic transition was reflected by the vibrational excitations of the hydrazino group observed in the 1C-R2PI spectrum. The band origin of the S1<--S0 transition is determined to be 33610 cm(-1) and the adiabatic ionization energy (IE) of phenylhydrazine, measured by 2C-R2PI spectroscopy, is 62829+/-15 cm(-1). The S1<--S0 electronic transitions of phenylhydrazine-Ar and phenylhydrazine-Ar2 complexes were also observed in the 1C-R2PI spectrum, and their band origins are, respectively, red-shifted by 39 and 80 cm(-1) from that of phenylhydrazine.

Cation spectroscopy and binding energy determination for 1,4-benzodioxan-Ar1 and -Ar2 complexes

Cation vibronic spectra are measured for 1,4-benzodioxan (BZD) and van der Waals complexes of BZD with one and two Ar atoms using zero electron kinetic energy and mass analyzed threshold ionization spectroscopy. The spectra of the monomer cation were used to measure the frequencies of the two key low-frequency modes which had previously been extensively studied in the neutral S0 and S1 states. The aliphatic ring twisting mode, nu25, has an energy of 146 cm(-1) in the cation, intermediate between the values found in the S0 and S1 states. The bending, butterfly-like mode nu48 has an energy of 125 cm(-1), which is of higher frequency than either of the neutral states. The S1 spectra of the BZD-Ar1 and BZD-Ar2 complexes are recorded and observed to have modest red shifts from the monomer. The cation spectra of the complexes are also measured using mass analyzed threshold ionization spectroscopy including scans at higher energy which are used to determine the Ar binding energies. The energies for the loss of one Ar atom were determined to be 630 +/- 10 and 650 +/- 10 cm(-1) for BZD-Ar and BZD-Ar2, respectively. The similar cation spectra and similar binding energies indicate that each Ar atom in BZD-Ar2 has a similar binding geometry. Quantum chemical calculations were performed which had fair agreement with the measured binding energies and give some insight into the specific binding geometry.