The broadening of a two-photon resonance is studied experimentally at the 4 s 1 S 0 −6 s 3 S 1 transition in a zinc atom upon absorption of two waves with a small detuning from an intermediate state in collisions with CO 2 , CO, and NO molecules. The measured absolute values of broadening cross sections greatly exceed gas-kinetic cross sections and are (9.4±2.4, 6.5±1.6, and 3.9±1.0)×10 − 14 cm 2 for CO 2 , CO, and NO, respectively. Anomalously large rate constants and cross sections obtained in experiments are explained by the efficient resonance quenching of the excited states of zinc atoms in collisions with molecules accompanied by transfer of the energy of excited atoms to vibrational-rotational degrees of freedom of molecules.The broadening of a two-photon resonance is studied experimentally at the 4 s 1 S 0 −6 s 3 S 1 transition in a zinc atom upon absorption of two waves with a small detuning from an intermediate state in collisions with CO 2 , CO, and NO molecules. The measured absolute values of broadening cross sections greatly exceed gas-kinetic cross sections and are (9.4±2.4, 6.5±1.6, and 3.9±1.0)×10 − 14 cm 2 for CO 2 , CO, and NO, respectively. Anomalously large rate constants and cross sections obtained in experiments are explained by the efficient resonance quenching of the excited states of zinc atoms in collisions with molecules accompanied by transfer of the energy of excited atoms to vibrational-rotational degrees of freedom of molecules.

Journal of Experimental and Theoretical PhysicsJan 1, 20040 citations

Transitions in Quantum Physical Systems—Cross Section

Arno Böhm

Springer eBooksJan 1, 19860 citations

Transitions in Quantum Physical Systems—Cross Section

Arno Böhm

Springer eBooksJan 1, 19790 citations

N2 - and CO-induced collisional broadening of forbidden ground-to-Rydberg-state transitions in sodium as measured by trilevel echoes

Ravinder Kachru, THOMAS W. MOSSBERG, Sven R. Hartmann

We report the first study of molecular-perturber-induced broadening of forbidden ground-to-Rydberg-state transitions. The ${\mathrm{N}}_{2}$ - and CO-induced-broadening cross sections for the $3S\ensuremath{-}\mathrm{nS} (\mathrm{nD})$ transitions of sodium have been measured for values of $n$ , the principal quantum number of the upper state, ranging from 4 to 41. These measurements, performed using the trilevel echo technique, were accomplished at sodium and perturber densities of ${10}^{\ensuremath{-}6}$ and 1 torr, respectively. The broadening rates, observed in the present experiment, differ in some respects from those observed previously with noble-gas perturbers. These differences, which presumably arise because of the presence of accessible internal degrees of freedom in the ${\mathrm{N}}_{2}$ and CO perturbers (and in the case of CO also because of its permanent electric-dipole moment), are most clearly displayed in $3S\ensuremath{-}\mathrm{nS}$ transitions. Previous work has shown that with noble-gas perturbers the $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections display a dramatic increase at low values of $n$ ; they then decline at intermediate values of $n$ , and at high $n$ they approach a limiting value. In the present experiment we find that the initial increase in $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections with $n$ is relatively small and more gradual. For high $n$ , the broadening cross sections become approximately constant. As is the case with noble-gas perturbers, the broadening of $3S\ensuremath{-}\mathrm{nD}$ transitions is generally larger than the broadening of the corresponding $3S\ensuremath{-}\mathrm{nS}$ transitions. With CO as a perturber, an unexplained irreproducibility in the broadening cross sections of high- $n$ $3S\ensuremath{-}\mathrm{nD}$ transitions is observed. One explanation has to do with the CO-induced frequency shifts being unusually large and exceeding the spectral width of our excitation lasers.We report the first study of molecular-perturber-induced broadening of forbidden ground-to-Rydberg-state transitions. The ${\mathrm{N}}_{2}$- and CO-induced-broadening cross sections for the $3S\ensuremath{-}\mathrm{nS} (\mathrm{nD})$ transitions of sodium have been measured for values of $n$, the principal quantum number of the upper state, ranging from 4 to 41. These measurements, performed using the trilevel echo technique, were accomplished at sodium and perturber densities of ${10}^{\ensuremath{-}6}$ and 1 torr, respectively. The broadening rates, observed in the present experiment, differ in some respects from those observed previously with noble-gas perturbers. These differences, which presumably arise because of the presence of accessible internal degrees of freedom in the ${\mathrm{N}}_{2}$ and CO perturbers (and in the case of CO also because of its permanent electric-dipole moment), are most clearly displayed in $3S\ensuremath{-}\mathrm{nS}$ transitions. Previous work has shown that with noble-gas perturbers the $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections display a dramatic increase at low values of $n$; they then decline at intermediate values of $n$, and at high $n$ they approach a limiting value. In the present experiment we find that the initial increase in $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections with $n$ is relatively small and more gradual. For high $n$, the broadening cross sections become approximately constant. As is the case with noble-gas perturbers, the broadening of $3S\ensuremath{-}\mathrm{nD}$ transitions is generally larger than the broadening of the corresponding $3S\ensuremath{-}\mathrm{nS}$ transitions. With CO as a perturber, an unexplained irreproducibility in the broadening cross sections of high-$n$ $3S\ensuremath{-}\mathrm{nD}$ transitions is observed. One explanation has to do with the CO-induced frequency shifts being unusually large and exceeding the spectral width of our excitation lasers.

Physical Review ANov 1, 19809 citations

Elastic scattering and inelastic transitions

J. Callaway, P. S. Laghos

Physics Letters AMar 1, 19685 citations

The He–CaH(2Σ+) interaction. II. Collisions at cold and ultracold temperatures

N. Balakrishnan, Gerrit C. Groenenboom, Roman V. Krems +1 more

We present cross sections for rotational, vibrational, and fine-structure transitions in He–CaH(2Σ) collisions at cold and ultracold temperatures calculated using the ab initio potential energy surface reported in the preceding paper. Rotational quenching is fast, vibrational quenching is slow. The spin-rotational interaction, although small and having no influence at temperatures above 10 K, changes significantly the rate coefficients for rotational quenching at lower temperatures. The theoretical rotational, vibrational, and elastic cross sections are compared with the results of a buffer gas cooling experiment carried out at a temperature of about 0.4 K. The theoretical predictions for the vibrational and elastic cross sections are larger than the measured values. The sensitivity to the potential energy surface is explored. A modified surface diminishes but does not remove the differences between theory and experiment.We present cross sections for rotational, vibrational, and fine-structure transitions in He–CaH(2Σ) collisions at cold and ultracold temperatures calculated using the ab initio potential energy surface reported in the preceding paper. Rotational quenching is fast, vibrational quenching is slow. The spin-rotational interaction, although small and having no influence at temperatures above 10 K, changes significantly the rate coefficients for rotational quenching at lower temperatures. The theoretical rotational, vibrational, and elastic cross sections are compared with the results of a buffer gas cooling experiment carried out at a temperature of about 0.4 K. The theoretical predictions for the vibrational and elastic cross sections are larger than the measured values. The sensitivity to the potential energy surface is explored. A modified surface diminishes but does not remove the differences between theory and experiment.

The Journal of Chemical PhysicsApr 11, 200380 citations

We report the first study of molecular-perturber-induced broadening of forbidden ground-to-Rydberg-state transitions. The

{\mathrm{N}}_{2}

- and CO-induced-broadening cross sections for the $3S\ensuremath{-}\mathrm{nS} (\mathrm{nD})$ transitions of sodium have been measured for values of

n

, the principal quantum number of the upper state, ranging from 4 to 41. These measurements, performed using the trilevel echo technique, were accomplished at sodium and perturber densities of ${10}^{\ensuremath{-}6}$ and 1 torr, respectively. The broadening rates, observed in the present experiment, differ in some respects from those observed previously with noble-gas perturbers. These differences, which presumably arise because of the presence of accessible internal degrees of freedom in the

{\mathrm{N}}_{2}

and CO perturbers (and in the case of CO also because of its permanent electric-dipole moment), are most clearly displayed in $3S\ensuremath{-}\mathrm{nS}$ transitions. Previous work has shown that with noble-gas perturbers the $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections display a dramatic increase at low values of

n

; they then decline at intermediate values of

n

, and at high

n

they approach a limiting value. In the present experiment we find that the initial increase in $3S\ensuremath{-}\mathrm{nS}$ broadening cross sections with

n

is relatively small and more gradual. For high

n

, the broadening cross sections become approximately constant. As is the case with noble-gas perturbers, the broadening of $3S\ensuremath{-}\mathrm{nD}$ transitions is generally larger than the broadening of the corresponding $3S\ensuremath{-}\mathrm{nS}$ transitions. With CO as a perturber, an unexplained irreproducibility in the broadening cross sections of high-

n

$3S\ensuremath{-}\mathrm{nD}$ transitions is observed. One explanation has to do with the CO-induced frequency shifts being unusually large and exceeding the spectral width of our excitation lasers.