Hydrogen bonds depletion spectroscopy

Recently25, some new tools have offered very important supports to infrared spectroscopy, as reported in the following instances. The infrared depletion spectrum of the aniline dimer, formed in a supersonic jet, indicates44,45 that two NH2 groups are equivalent. One possible structure is a sandwich, with the N—H n hydrogen bonds, with two aniline molecules arranged head to tail, as shown in 1. 

D. Intermolecular Hydrogen Bonds of Aniline Cation Infrared Depletion Spectroscopy... 

Aniline clusters and the corresponding clusters with N2, CH4, CHF3 and CO are studied by detecting the depletion of resonance-enhanced multiphoton ionization spectroscopy (with time-of-flight mass spectrometer) which measures the vibrational spectra of the complexes. The interaction in clusters involving aniline cation is different from that of neutral aniline. The hydrogen bonding interaction is the main interaction in the aniline cation cluster, while neutral aniline clusters are due to van der Waals interaction. 

The infrared depletion spectroscopy of the aniline/toluene cluster makes it possible to measure the NH2 stretching vibration185. The two main possibilities which are derived from the calculated structure of the aniline/toluene and [aniline/toluene]4 clusters are depicted respectively in 115 and 116. An N—H - it hydrogen bond is the main interaction in both cases. 

Aniline/NH3 and [aniline/NH3]+ clusters are studied by infrared depletion spectroscopy. In both cases the hydrogen bond is between the NH of the aniline and the lone pair of NH3. In the cation cluster the interaction is much stronger than in the neutral cluster201. 

In infrared depletion spectroscopy of the neutral aniline/pyrrole205 complex, both spectroscopic observation and theoretical calculations indicate the presence of a hydrogen bond between one of the N—H bonds of aniline and the n system of pyrrole, as illustrated in 129. 

Cavity ring down (CRD) spectroscopy, having proven to be a very sensitive method for detecting molecular species in a wide variety of environments, has also been applied to the mid infrared vibrational spectroscopy of hydrogen-bonded clusters of water " and alcohols.As a direct absorption method, it can be used to quantitatively measure important molecular properties, such as absorption cross sections and coefficients. Knowing these properties, as a function of cluster size and structure, is useful in making the connection to the condensed phase. The sensitive detection of methanol clusters, as shown in Fig. 13, is of considerable importance. These particular measurements nicely complement the action spectra of methanol clusters, detected by depletion of mass-detected signal via vibrational predissociation. 

Infrared depletion spectroscopy suggests fast vibrational relaxation in the hydrogen-bonded aniline-tetrahydrofiiran (C6H5NH2- OC4H8) complex ... 

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