TY - JOUR
T1 - Coupled translation-rotation eigenstates of H2 in C60 and C70 on the spectroscopically optimized interaction potential
T2 - Effects of cage anisotropy on the energy level structure and assignments
AU - Xu, Minzhong
AU - Sebastianelli, Francesco
AU - Gibbons, Brittney R.
AU - Bačić, Zlatko
AU - Lawler, Ronald
AU - Turro, Nicholas J.
N1 - Funding Information:
We thank the authors of Ref. 22 for early communication of the results prior to their publication. Z.B. is grateful to the National Science Foundation for partial support of this research through Grant No. CHE-0315508. The computational resources used in this work were funded in part by the NSF MRI Grant No. CHE-0420870. Acknowledgment is made to the donors of the American Chemical Society Petroleum Research Fund for partial support of this research. N.J.T. thanks the NSF for support of this research through Grant No. CHE-0717518.
PY - 2009
Y1 - 2009
N2 - We have developed a quantitatively accurate pairwise additive five-dimensional (5D) potential energy surface (PES) for H2 in C 60 through fitting to the recently published infrared (IR) spectroscopic measurements of this system for H2 in the vibrationally excited ν=1 state. The PES is based on the three-site H2 -C pair potential introduced in this work, which in addition to the usual Lennard-Jones (LJ) interaction sites on each H atom of H2 has the third LJ interaction site located at the midpoint of the H-H bond. For the optimal values of the three adjustable parameters of the potential model, the fully coupled quantum 5D calculations on this additive PES reproduce the six translation-rotation (T-R) energy levels observed so far in the IR spectra of H2 @ C60 to within 0.6%. This is due in large part to the greatly improved description of the angular anisotropy of the H2 -fullerene interaction afforded by the three-site H2 -C pair potential. The same H2 -C pair potential spectroscopically optimized for H2 @ C60 was also used to construct the pairwise additive 5D PES of H2 (ν=1) in C70. This PES, because of the lower symmetry of C70 (D5h) relative to that of C60 (Ih), exhibits pronounced anisotropy with respect to the direction of the translational motion of H2 away from the cage center, unlike that of H2 in C60. As a result, the T-R energy level structure of H2 in C70 from the quantum 5D calculations on the optimized PES, the quantum numbers required for its assignment, and the degeneracy patterns which arise from the T-R coupling for translationally excited H2 are all qualitatively different from those determined previously for H2 @ C60 [M. Xu, J. Chem. Phys. 128, 011101 (2008).
AB - We have developed a quantitatively accurate pairwise additive five-dimensional (5D) potential energy surface (PES) for H2 in C 60 through fitting to the recently published infrared (IR) spectroscopic measurements of this system for H2 in the vibrationally excited ν=1 state. The PES is based on the three-site H2 -C pair potential introduced in this work, which in addition to the usual Lennard-Jones (LJ) interaction sites on each H atom of H2 has the third LJ interaction site located at the midpoint of the H-H bond. For the optimal values of the three adjustable parameters of the potential model, the fully coupled quantum 5D calculations on this additive PES reproduce the six translation-rotation (T-R) energy levels observed so far in the IR spectra of H2 @ C60 to within 0.6%. This is due in large part to the greatly improved description of the angular anisotropy of the H2 -fullerene interaction afforded by the three-site H2 -C pair potential. The same H2 -C pair potential spectroscopically optimized for H2 @ C60 was also used to construct the pairwise additive 5D PES of H2 (ν=1) in C70. This PES, because of the lower symmetry of C70 (D5h) relative to that of C60 (Ih), exhibits pronounced anisotropy with respect to the direction of the translational motion of H2 away from the cage center, unlike that of H2 in C60. As a result, the T-R energy level structure of H2 in C70 from the quantum 5D calculations on the optimized PES, the quantum numbers required for its assignment, and the degeneracy patterns which arise from the T-R coupling for translationally excited H2 are all qualitatively different from those determined previously for H2 @ C60 [M. Xu, J. Chem. Phys. 128, 011101 (2008).
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U2 - 10.1063/1.3152574
DO - 10.1063/1.3152574
M3 - Article
C2 - 19530767
AN - SCOPUS:67549099358
SN - 0021-9606
VL - 130
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 22
M1 - 224306
ER -