R. James Cross

Putting Ammonia into a Chemically Opened Fullerene

We put ammonia into an open-cage fullerene with a 20-membered ring ( 1) as the orifice and examined the properties of the complex using NMR and MALDI-TOF mass spectroscopy. The proton NMR shows a broad resonance corresponding to endohedral NH 3 at delta H = -12.3 ppm relative to TMS. This resonance was seen to narrow when a (14)N decoupling frequency was applied. MALDI spectroscopy confirmed the presence of both 1 ( m/ z = 1172) and 1 + NH 3 ( m/ z = 1189), and integrated intensities of MALDI peak trains and NMR resonances indicate an incorporation fraction of 35-50% under our experimental conditions. NMR observations showed a diminished incorporation fraction after 6 months of storage at -10 degrees C, which indicates that ammonia slowly escapes from the open-cage fullerene.

Some new diatomic molecule containing endohedral fullerenes

Abstract Several new diatomic molecule-containing endohedral fullerenes were prepared by heating C 60 or C 70 under high pressures of the corresponding gases. The species prepared are N 2 @C 60 , N 2 @C 70 , 13 CO@C 60 , and 3 He 22 Ne@C 70 . Their existence was demonstrated through high sensitivity, wide dynamic range mass spectrometry. Out of two thousand C 60 molecules about one is observed to incorporate N 2 . The nitrogen molecule containing endohedral molecules are stable and the mass spectrometric signal is not lost even after several hours heating at 500 K. The corresponding endohedral ions undergo the Rice shrink-wrap mechanism; a mass-analyzed ion kinetic energy spectrum demonstrates the loss of a C 2 unit from the cage. The observation of 13 CO@C 60 by mass spectrometry opens up the possibility for future NMR studies of this molecule. The observation of 3 He 22 Ne@C 70 is in accordance with the “promoter” mechanism of Thiel and co-worker [J. Am. Chem. Soc. 118 (1996) 7164; Helv. Chim. Acta 80 (1997) 495], whereby the singly and doubly occupied fullerenes are in equilibrium but the empty and filled fullerenes are not.

Methane in an open-cage [60]fullerene.

An endohedral methane complex of a fullerene derivative is first synthesized by insertion of a methane molecule through the opening of an open-cage C(60) derivative. The trapped methane is confirmed by NMR spectroscopy and mass spectrometry. Both methane carbon and protons show remarkable upfield shifts in NMR, characteristic of a chemical species in a fullerene cage. CH(4) protons appear as one equivalent signal in the (1)H NMR spectrum, suggesting that even methane can rotate in a C(60) cage.

Competition between charge exchange and chemical reaction - The D2/+/ + H system

The trajectory surface hopping (TSH) model was used to study the competition between chemical reaction and charge exchange for the reactions D2+ + H → D2 + H+, DH + D+, D + H + D+, D + D + H+. The three adiabatic surfaces, one triplet and two singlet, which are needed to describe this system are computed using the diatomics‐in‐molecules‐zero‐overlap approximation. Cross sections and the reaction dependence on impact parameter are obtained as a function of initial vibrational quantum number at the relative energy of 2 eV. The chemical reaction is found to depend in part on surface crossings and the charge exchange on chemical interactions. The results are discussed as a prototype of this sort of competition.

Putting atoms and molecules into chemically opened fullerenes.

We studied Ar, Kr, CO, and N(2) going into and out of a chemically opened fullerene, 1. We measured the equilibrium constant, K(eq), for the formation of X@1. K(eq) is particularly large for Ar, probably due to the large van der Waals attraction between the Ar atom and the fullerene cage. We measured rate constants and activation energies for the unimolecular reaction X@1-->X + 1 (X = Ar, CO, N(2)). The reactions show an unusually small pre-exponential factor, probably due to the loose binding of X inside the cage.

An artificial molecule of Ne2 inside C70

Abstract C 70 was heated with 22 Ne at high pressure. Analysis by mass spectrometry unexpectedly showed the formation of Ne 2 @C 70 in addition to Ne@C 70 . The ratio of empty C 70 to mono-occupied to di-occupied was 1000:1:0.02. A mechanism where a small fraction of the fullerene breaks open and reaches equilibrium with the neon and then closes is suggested to explain these results.

Vibrationally inelastic scattering at high energies: H++H2

The sudden approximation is used to compute integral and differential cross sections for H++H2(v=0) →H++H2(v′=1–4) using an ab initio DIMZO (diatomics‐in‐molecules, zero overlap) potential‐energy surface. Good agreement was obtained above 100 eV with calculations of Gentry and Giese using the DECENT approximation. Agreement with the experiments of Hererro and Doering seems fair if their data are properly analyzed. Several useful numerical approximations are developed and tested. These result in savings of several orders of magnitude in computation time.

Direct detection and quantitation of He@C60 by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry.

In this paper, we report negative ion microelectrospray Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry of C60 samples containing ∼1% 3He@C60 or 4He@C60. Resolving 3He@C60− and 4He@C60− from C60 containing 3 or 4 13C instead of 12C atoms is technically challenging, because the target species are present in low relative abundance and are very close in mass. Nevertheless, we achieve baseline resolution of 3He@C60− from 13C312C57− and 4He@C60− from 13C412C56− in single-scan mass spectra obtained in broadband mode without preisolation of the ions of interest. The results constitute the first direct mass spectrometric observation of endohedral helium in a fullerene sample at this (low) level of incorporation. The results also demonstrate the feasibility of determining the extent of He incorporation from the FT-ICR mass spectral peak heights. The present measurements are in agreement with those obtained by the pyrolysis method [1–3]. Although limited in sensitivity, the mass spectral method is faster and easier than pyrolysis.

Reaction of cyclopropa[b]naphthalene with 3He@C60

The adduct (I) formed by the reaction of the diradical obtained by heating cyclopropa[b]naphthalene with 3He-labeled C60 has been characterized. The corresponding 1h, 13C, and 3He NMR spectra are reported.

Vibration-rotation spectroscopy of molecules trapped inside C60.

A simple model is developed to treat the energy levels and spectroscopy of diatomic molecules inside C 60. The C 60 cage is treated as spherically symmetric, and the coupling to the C 60 vibrations is ignored. The remaining six degrees of freedom correspond to the vibrations and rotations of the diatomic molecule and the rattling vibration of the molecule inside the cage. By using conservation of angular momentum, we can remove two of these motions and simplify the calculations. The resulting energy levels are simple and can be labeled by a set of quantum numbers. The IR and Raman spectra look like those of gas-phase diatomic molecules at low temperatures. At higher temperatures, hot bands due to the low-frequency rattling mode appear, and the spectrum becomes congested, looking like a solution spectrum.