State-to-State Rotational Excitation of CO by H\u3csub\u3e2\u3c/sub\u3e Near 1000 cm\u3csup\u3e-1\u3c/sup\u3e Collision Energy

Relative state-to-state rotationally inelastic cross sections for excitation of carbon monoxide by hydrogen were measured in a crossed molecular beam experiment at collision energies 795, 860, and 991 cm-1. The results are compared to predictions of a recent ab initio potential energy surface [J. Chem. Phys. 108, 3554 (1998)]. The agreement is very good. A comparison with older data on thermally averaged total depopulation cross sections [Chem. Phys. 53, 165 (1980)] indicates that the absolute magnitudes of the cross sections predicted by the surface are too high. The CO excitation is dominated by collisions that are elastic in H2 rotation, and the collision dynamics are very similar for different rotational levels of hydrogen

State to State He-CO Rotationally Inelastic Scattering

Relative integral cross sections for rotational excitation of CO in collisions with He were measured at energies of 72 and 89 meV. The cross sections are sensitive to anisotrophy in the repulsive wall of the He-CO interaction. The experiments were done in crossed molecular beams with resonance enhanced multiphoton ionization detection. The observed cross sections display interference structure at low Δj, despite the average over the initial CO rotational distribution. At higher Δj, the cross sections decrease smoothly. The results are compared with cross sections calculated from two high quality potential energy surfaces for the He-CO interaction. The ab initio SAPT surface of Heijmen et al. [J. Chem. Phys. 107, 9921 (1997)] agrees with the data better than the XC(fit) surface of Le Roy et al. [Farad. Disc. 97, 81 (1994)]

State to State Ne-CO Rotationally Inelastic Scattering

Measurements of state-to-state integral cross sections for rotational excitation of CO by collisions with Ne are reported. The measurements were performed in crossed molecular beams with resonance enhanced multiphoton detection at collision energies of 711 and 797 cm-1. The cross sections display strong interference structure, with a propensity for odd Δj below Δj=10. Predictions of the ab initio potential surface of Moszynski et al. [J. Phys. Chem. A 101, 4690 (1997)] and the new ab initio surface of McBane and Cybulski [J. Chem. Phys. 110, 11734 (1999), preceding paper] are compared to the data. The new surface agrees more closely with the observed interference structure, although significant disagreements remain

RELATIVE INTEGRAL CROSS SECTIONS FOR T→RT \rightarrow R ENERGY TRANSFER IN He-CO COLLISIONS

Author Institution: Department of Chemistry, The Ohio State University$T \rightarrow R$ energy transfer between He and CO has been studied in a crossed beam experiment. CO was initially prepared in its lowest few rotational states by seeded supersonic expansion. Postcollision populations of higher CO rotational states were determined with resonance enhanced multiphoton ionization. Extraction of populations and cross sections from the REMPI signal intensities, comparisons with related experiments, and implications for the He-CO potential surface will be presented

MULTIPLE RESONANCE SPECTROSCOPY OF THE G1ΠgG^{1}\Pi_{g} AND F1Σg+F^{1}\Sigma^{+}_{g} STATES OF 7Li2^{7}Li_{2} DETECTION OF PREDISSOCIATING F1Σg+F^{1}\Sigma^{+}_{g} STATE LEVELS THROUGH ATOMIC SIDE FLUORESCENCE

Author Institution: Physics Department, Temple University; Department of Modern Applied Physics, Tsinghua UniversityOptical-Optical Double Resonance (OODR) was employed to excite rovibrational levels in the unknown upper portions of the G(1)$^{1}\Pi_{g}$ and F(4)$^{1}\Sigma^{+}_{g}$ states. Although both are singlet states and dissociate to the same atomic limit (2p+2p) they behave in significantly different ways. Vibrational levels as high as v = 48, which has rotationless energy within 1% from the dissociation energy, were observed in the $G^{1}\Pi_{g}$ state by detecting molecular fluorescence. In the $F^{1}\Sigma^{+}_{g}$ state all levels in the energy region above 2s+3s atomic limit were found to the strongly predissociated. This is due to interactions with the continuum of the $E^{1}\Sigma^{+}_{g}$ state which at long internuclear distance dissociates to the 2s + 3s atomic limit. Because of the very short lifetimes these levels were detected using atomic side fluorescence. A $C_{5}$ coefficient was determined from the last few outer turning points of the experimental RKR potential curve of the $G^{1}\Pi_{g}$ state. Rotational and vibrational dependence of the line width for the predissociated $F^{1}\Sigma^{+}_{g}$ state levels was investigated and a preliminary RKR curve which covers 99.6% of the potential well has been derived from experimental data