^{1,a)}, Hsu Chen Hsu

^{1,b)}, Yuan Chin Hsu

^{1,a)}and Chi-Kung Ni

^{1,a),c)}

### Abstract

The vibrational energy dependence, H and D atom isotope effects, and the mass effects in the energy transfer between rare gas atoms and highly vibrationally excited naphthalene in the triplet state were investigated using crossed-beam/time-sliced velocity-map ion imaging at various translational collision energies. Increase of vibrational energy from does not make a significant difference in energy transfer. The energy transfer properties also remain the same when H atoms in naphthalene are replaced by D atoms, indicating that the high vibrational frequency modes do not play important roles in energy transfer. They are not important in supercollisions either. However, as the Kr atoms are replaced by Xe atoms, the shapes of energy transferprobability density functions change. The probabilities for large translation to vibration/rotation energy transfer and large vibration to translation energy transfer decrease. High energy tails in the backward scatterings disappear, and the probability for very large vibration to translation energy transfer such as supercollisions also decreases.

This work was partly supported by the National Science Council, Taiwan, under Contract No. NSC95-2113-M-001. We thank Professor Y. T. Lee and I. Oref for many helpful discussions.

I. INTRODUCTION

II. EXPERIMENT

III. RESULTS AND DISCUSSION

A. Vibrational energy dependence

B. H and D atom isotope effects

C. Mass effects

### Key Topics

- Energy transfer
- 86.0
- Probability density functions
- 18.0
- Vibrational energy transfer
- 18.0
- Atomic and molecular beams
- 13.0
- Ultraviolet light
- 7.0

## Figures

Angular resolved energy transfer probability density functions (double differential cross section with respect to solid angle and transferred energy) of naphthalene excited by 266 and in collisions with Kr at various collision energies. Thick black line, thin black line, and dot black line represent near forward, sideway, and backward density functions excited by ; thick gray line, thin gray line, and dot gray line represent near forward, sideway, and backward density functions excited by . The first column represents the up collisions energy transfer; the second column represents the down collisions energy transfer. The third column shows the region of maximum down collisions energy transfer. The density functions at each collision energy for each pump wavelength are normalized separately so that . In each plot, the density functions for 266 and are plotted in the same scale.

Angular resolved energy transfer probability density functions (double differential cross section with respect to solid angle and transferred energy) of naphthalene excited by 266 and in collisions with Kr at various collision energies. Thick black line, thin black line, and dot black line represent near forward, sideway, and backward density functions excited by ; thick gray line, thin gray line, and dot gray line represent near forward, sideway, and backward density functions excited by . The first column represents the up collisions energy transfer; the second column represents the down collisions energy transfer. The third column shows the region of maximum down collisions energy transfer. The density functions at each collision energy for each pump wavelength are normalized separately so that . In each plot, the density functions for 266 and are plotted in the same scale.

Angular resolved energy transfer probability density functions for naphthalene- and naphthalene- in collisions with Kr at two collision energies. Thick black line, thin black line, and black dot line represent near forward, sideway, and backward density functions for naphthalene-; thick gray line, thin gray line, and gray dot line represent near forward, sideway, and backward density functions for naphthalene-. Collision energies are 564 and for naphthalene- and naphthalene-, respectively, in (a)–(c); they are 853 and for -naphthalene and -naphthalene, respectively, in (d)–(f). The first column represents the up collisions energy transfer; the second column represents the down collisions energy transfer. The third column shows the region of maximum down collisions energy transfer. Both naphthalene- and naphthalene- are excited by photons. The density functions at each collision energy are normalized so that . In each plot, naphthalene- and naphthalene- are plotted in the same scale.

Angular resolved energy transfer probability density functions for naphthalene- and naphthalene- in collisions with Kr at two collision energies. Thick black line, thin black line, and black dot line represent near forward, sideway, and backward density functions for naphthalene-; thick gray line, thin gray line, and gray dot line represent near forward, sideway, and backward density functions for naphthalene-. Collision energies are 564 and for naphthalene- and naphthalene-, respectively, in (a)–(c); they are 853 and for -naphthalene and -naphthalene, respectively, in (d)–(f). The first column represents the up collisions energy transfer; the second column represents the down collisions energy transfer. The third column shows the region of maximum down collisions energy transfer. Both naphthalene- and naphthalene- are excited by photons. The density functions at each collision energy are normalized so that . In each plot, naphthalene- and naphthalene- are plotted in the same scale.

Angular resolved energy transfer probability density functions of naphthalene excited by in collisions with Xe at various collision energies. Thick black line, thin black line, and gray line represent near forward, sideway, and backward probability density functions. The first column represents the up collisions energy transfer; the second column represents the down collisions energy transfer. The third column shows the region of maximum down collisions energy transfer. The density functions at each collision energy are normalized separately so that .

Angular resolved energy transfer probability density functions of naphthalene excited by in collisions with Xe at various collision energies. Thick black line, thin black line, and gray line represent near forward, sideway, and backward probability density functions. The first column represents the up collisions energy transfer; the second column represents the down collisions energy transfer. The third column shows the region of maximum down collisions energy transfer. The density functions at each collision energy are normalized separately so that .

Energy transfer probability density functions in collisions with Xe at various collision energies. Thin black line: ; gray line: ; thick black line: . Negative values represent down collisions energy transfer and positive values represent up collisions energy transfer. The density functions at each collision energy are normalized separately so that .

Energy transfer probability density functions in collisions with Xe at various collision energies. Thin black line: ; gray line: ; thick black line: . Negative values represent down collisions energy transfer and positive values represent up collisions energy transfer. The density functions at each collision energy are normalized separately so that .

## Tables

Velocity uncertainties and speed ratios of naphthalene molecular beam. and are the full widths at half maximum of the naphthalene velocity distribution in the and directions, respectively. is the naphthalene velocity in the laboratory frame, is the naphthalene velocity in the center-of-mass frame, , is the uncertainty of collision energy, and .

Velocity uncertainties and speed ratios of naphthalene molecular beam. and are the full widths at half maximum of the naphthalene velocity distribution in the and directions, respectively. is the naphthalene velocity in the laboratory frame, is the naphthalene velocity in the center-of-mass frame, , is the uncertainty of collision energy, and .

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