Neutral and negatively-charged formamide, N-methylformamide and dimethylformamide clusters

Infrared spectroscopy of mass-selected neutral molecular systems without chromophore: the formamide monomer and dimer

“…The calculated lowest energy configuration of the neutral formamide complex is a head-to-tail cyclic configuration with a null total dipole moment but a rather large positive quadrupole moment, Q ¼ þ48 DÅ , that allows for the formation of stable quadrupole-bound anions (QBA), as studied in previous RET experiments [8,15]. This double H-bond structure corresponds to a high dissociation energy, calculated to be D 0 ¼ 475 meV, i.e.…”

“…Electron transfer takes place in the collision region between the laser-excited atoms and the neutral molecular beam and monomer or dimer anions are produced, accelerated and detected at the end of a linear time-of-flight mass spectrometer. By tuning the wavelength of the laser responsible for the excitation of the Rydberg atoms and thus their principal quantum number n, we optimize either the monomer or the dimer anion formation rates, which are respectively peaked at n ¼ 13 [7] and n ¼ 15 [8]. Once either monomer or dimer anion signals are optimized, we cross the neutral molecular beam with the IR laser beam issued from a tuneable infrared OPO (optical parametric oscillator), upstream from the ionization region and a few hundred nanoseconds before the Rydberg excitation laser.…”

Long-Range Electron Binding to Quadrupolar Molecules

“…On the experimental side, there has been no firm evidence for the existence of weakly bound anions due to the quadrupolar interactions alone. Experimental data, from Rydberg electron transfer to the formamide dimer 9 and photoelectron spectroscopy of MgO cluster anions 8 have been interpreted in terms of quadrupolebound anions. However, it can be argued that these interpretations might not be valid due to the lack of theoretical support in the formamide case and to rather well localized orbitals, close to Mg atoms, in the case of MgO clusters, with rather large EA values (0.5 -1 eV).…”

“…From the peak values of the RET curve, and with the help of a semi-empirical law verified for a large number of weakly bound anions 17 , EA = 23 eV / n * 2.8 , we derive the EA-values of 115 meV (n * = 6.65) and 22 meV (n * = 12), for the excess electron binding energies. Fitting the experimental curve with a simple curve-crossing model for RET [9] provides the first indication that the main peak cannot correspond to dipole-bound anion formation. On the other hand, the small peak at low n * is likely to correspond to dipole-bound gauche anion formation, as also strongly suggested from photoelectron spectroscopy data obtained at JHU which give an EA of 108 ± 10 meV for SN anions produced directly in the micro-plasma at the beam exit.…”

Kinetically Controlled Formation of Formamide Trimer from First Principles

“…[16] Small (FMA) n clusters have been investigated experimentally by electron attachment spectroscopy. [17][18][19] Scheier and coworkers recently observed an anomalous helium affinity for the dimer anion which they loosely correlated to the structure of the neutral parent. [17] They suggested that in cold helium matrices the predominant dimer species is likely to be highly polar.…”