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

Abstract

The paper presents IR spectroscopic data and theoretical frequency calculations, in the C-H and N-H stretch region, on jet-cooled formamide molecules and dimers. By using dipolebound or quadrupole-bound anion formation, one is able to monitor IR absorption in the neutral beam on mass-selected species. For isolated formamide, resonant IR excitation leads to autodetachment of the excess electron in the dipole-bound anion. For the formamide dimer, the IR spectrum is characteristic from the cyclic dimer, with two neighbouring bonded N-H stretches and a complex spectrum with several lines and a broad absorption band in the C-H region absorption, as for the cyclic formic acid dimer. In this double H-bond configuration, IR absorption cannot lead to vibrational predissociation but it probably produces hot neutral dimers with large-amplitude intermolecular motions that reinforce autodetachment of the nascent weakly bound anions. Thus, the present original IR spectroscopic technique, which allows for rigorous mass-selection of the neutrals, seems to be relevant for any polar neutral species.

Using the reaction force and the reaction electronic flux on the proton transfer of formamide derived systems

“…It is characterized by some specific properties like the coplanarity of the groups attached to the nitrogen atom, a high rotational barrier and kinetic stability toward nucleophilic attack or hydrolysis. 8,9 The formamide dimer has been studied extensively by theoretical [10][11][12][13][14][15][16][17][18][19][20][21][22][23] and experimental [24][25][26] methods. The double proton transfer in the formamide dimer occurs concertedly both in the gas phase and in solution.…”

Size-Dependent Metamorphosis of Electron Binding Motif in Cluster Anions of Primary Amide Molecules

“…Three-dimensional network arrangements similar to those in condensed phases − are not appropriate for the clusters because these make a large number of dangling NH groups free from hydrogen bonding for a finite size of aggregation. A great abundance of the antiparallel dimer in a supersonic jet has been revealed by infrared absorption spectroscopy. , The ladder-like arrangements of the dimer units are the most efficient to gain a number of hydrogen bonds, minimizing dangling NH groups to 2 at both the ladder ends. Figure shows the structures optimized with the B3LYP/6-311++G(d,p) level calculations for neutral AA clusters of n = 5 and 6.…”

“…A great abundance of the antiparallel dimer in a supersonic jet has been revealed by infrared absorption spectroscopy. 31,32 The ladder-like arrangements of the dimer units are the most efficient to gain a number of hydrogen bonds, minimizing dangling NH groups to 2 at both the ladder ends. Figure 3 shows the structures optimized with the B3LYP/ 6-311++G(d,p) level calculations for neutral AA clusters of n = 5 and 6.…”

Vibrational spectroscopy of size-selected neutral and cationic clusters combined with vacuum-ultraviolet one-photon ionization detection

“…While spectroscopic investigations for protonated cluster cations 86,87 and cluster anions 88 of FA have extensively been carried out, neutral clusters of FA have undergone only few spectroscopic investigations. 89,90 Because FA has no UV chromophore, FA is a typical example which the conventional IR-UV double resonance spectroscopy is inapplicable to. Successful observations of the IR spectra of FA-H 2 O and (FA) 2 have been uniquely reported by Schermann and coworkers through a development of IR dissociation/electron detachment spectroscopy based on their Rydberg electron transfer (RET) technique.…”

“…Successful observations of the IR spectra of FA-H 2 O and (FA) 2 have been uniquely reported by Schermann and coworkers through a development of IR dissociation/electron detachment spectroscopy based on their Rydberg electron transfer (RET) technique. 89,90 Systematic and size-selective spectroscopic studies for FA-(H 2 O) n , n 41, however, have never been reported. VUV-ID-IRPDS is developed for vibrational spectroscopies of such neutral clusters without a UV chromophore, 49 and its application to FA-(H 2 O) n , n = 1-4, well demonstrates the potential of this new method.…”