Interaction potential and infrared absorption of endohedral H2 in C60

Abstract

We have measured the temperature dependence of the infrared spectra of a hydrogen molecule trapped inside a C 60 cage, H 2 @C 60 , in the temperature range from 6 to 300 K and analyzed the excitation spectrum by using a five-dimensional model of a vibrating rotor in a spherical potential. The electric dipole moment is induced by the translational motion of endohedral H 2 and gives rise to an infrared absorption process where one translational quantum is created or annihilated, N = ±1. Some fundamental transitions, N = 0, are observed as well. The rotation of endohedral H 2 is unhindered but coupled to the translational motion. The isotropic and translation-rotation coupling part of the potential are anharmonic and different in the ground and excited vibrational states of H 2 . The vibrational frequency and the rotational constant of endohedral H 2 are smaller than those of H 2 in the gas phase. The assignment of lines to ortho-and para-H 2 is confirmed by measuring spectra of a para enriched sample of H 2 @C 60 and is consistent with the earlier interpretation of the low temperature infrared spectra [Mamone et al., J. Chem. Phys. 130, 081103 (2009)].

The dipolar endofullerene HF@C60

“…The change in the fundamental vibrational transition (-170.5 cm -1 ) is in excellent agreement with that calculated by Dolgonos (-174 cm -1 ), 17 31 The rotational redshifts are attributed to a coupling of translational and rotational modes inside the cavity, and to cage-host interactions, which cause the inertial moment of the HF molecule to acquire some of the effective mass of the cage. The vibrational red-shift is due to lengthening, of the bond of the enclosed diatomic molecule indicating an attractive interaction with the cage.…”

“…The translational modes are defined by the motion of the center of mass of HF within its cage, resembling a three-dimensional quantum oscillator. 31,32 Therefore quantization of the vibrational, rotational and translational excitations is defined by the quantum numbers v = 0, 1.., J = 0, 1.., and N = 0, 1.., respectively. 33,34 An energy level diagram for the confined rotor is shown in Figure 3(c).…”

Interstellar fullerene compounds and diffuse interstellar bands

“…the review by Vehvilainen et al 2011), including, for example, infrared spectroscopy (Mamone et al 2009(Mamone et al , 2011Ge et al 2011), inelastic neutron scattering (Vehvilainen et al 2011), and NMR studies (Murata et al 2006;Turro et al 2010).…”

HD in C 60 : theoretical prediction of the inelastic neutron scattering spectrum and its temperature dependence

“…The three translational degrees of freedom of the incarcerated H 2 /HD are quantized and their eigenstates are well separated in energy. The same holds for the quantized rotational levels of H 2 /HD owing to their exceptionally large rotational constants, 7.24 and 5.52 meV in the ground vibrational state, inside C 60 [4]. This gives rise to a very sparse translation-rotation (T-R) energy level structure.…”

“…Shortly thereafter, the first infrared (IR) spectra measured for H 2 @C 60 [6] showed absorption lines split into distinct peaks owing to the T-R coupling, as predicted by our calculations [2,3]. Subsequent IR spectroscopic studies of H 2 @C 60 [4] as well as of endohedral HD and D 2 in C 60 [7] have provided a great deal of valuable information about the T-R energy levels of the guest molecules and their interaction potentials with C 60 . The physical properties of hydrogen endofullerenes have also been probed by nuclear magnetic resonance [1,8,9].…”