The tuning range and bandwidth of an ArF laser were measured using 1 + 1 resonantly enhanced multiphoton ionization of NO. Operated as an injection-seeded oscillator/amplifier combination, the tuning range was 51,560-51,810 cm(-1); operated with single pass amplification of the oscillator, the tuning range was 51,560-51,765 cm(-1). In both cases, the laser bandwidth, determined from the linewidth, was 0.21 +/- 0.06 cm(-1). Rotational lines in the beta(7,0), gamma(3,O), and epsilon(0,1) bands were observed including several previously unreported lines.

The absolute two-photon excitation cross section for the ${\mathrm{H}}_{2}$ E,F $^{1}\ensuremath{\Sigma}_{g}$ (v'=6)\ensuremath{\leftarrow}${\mathrm{X}}^{1}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}$ (v''=0) Q(1) transition at 193 nm has been measured by observing the E,F $^{1}\ensuremath{\Sigma}_{g}^{+}$ (v'=6)->B $^{1}\ensuremath{\Sigma}_{u}^{+}$ (v''=0) fluorescence at \ensuremath{\sim}750 nm. The measured integrated two-photon excitation cross section, (2.0\ifmmode\pm\else\textpm\fi{}0.9)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}36}$ ${\mathrm{cm}}^{4}$, is in good agreement with the theoretical value of 2.8\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}36}$ ${\mathrm{cm}}^{4}$, which is obtained from previously published calculations [Huo and Jaffe, Chem. Phys. Lett. 101, 463 (1983)]. The absolute cross section for photoabsorption by the E,F state at 355 and 193 nm was also measured by monitoring the depletion of the 750-nm fluorescence caused by a second laser. The measured cross sections for photoabsorption by the E,F (v=6) state are (9.7\ifmmode\pm\else\textpm\fi{}2.4)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$ at 355 nm and (6.4\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$ at 193 nm. Comparison with theoretical estimates [Cohn, J. Chem. Phys. 57, 2456 (1972)] of the direct photoionization cross section of this state (8.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$ at 355 nm and 3.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$ at 193 nm) suggests that other processes may contribute to the photoabsorption.Photoexcitation of the dissociating $^{1}\mathrm{\ensuremath{\Sigma}}_{\mathrm{u}}$ autoionizing state is found to be important. Cross sections for this additional channel, which may lead to dissociation (${\mathrm{H}}^{\mathrm{*}}$+H or ${\mathrm{H}}^{+}$+${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$) or autoionization (${\mathrm{H}}_{2}^{+}$+${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$), are calculated to be 3.6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$ at 355 nm and 7.6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$ at 193 nm. The calculated branching ratio strongly favors dissociation at 355 nm and autoionization at 193 nm.

Absolute two-photon absorption cross sections have been measured for the np $^{3}P_{2}$,1,0\ensuremath{\leftarrow}2p $^{3}\mathrm{P}_{2}$ transitions in atomic oxygen (n=4 and 5) using the technique of two-photon--excited fluorescence. For the n=4 transition at 200.6 nm the integrated cross section is ${\mathcal{J}}_{J\mathcal{'}}$${\ensuremath{\sigma}}_{0}^{(2)}$(J'\ensuremath{\leftarrow}2) =(4.8\ifmmode\pm\else\textpm\fi{}2.4)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}36}$ ${\mathrm{cm}}^{4}$. The corresponding number for the n=5 transition at 192.5 nm is (0.${7}_{\ensuremath{-}0.5}^{+0.7}$)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}36}$ ${\mathrm{cm}}^{4}$. These numbers are in moderately good agreement with ab initio calculations presented previously [Phys. Rev. A 34, 199 (1986)] for n=4 and in this paper for n=5. Calculations are also reported for the 4f $^{3}F_{4}$,3,2\ensuremath{\leftarrow}2p $^{3}\mathrm{P}_{\mathrm{J}\mathcal{'}\mathcal{'}}$ transition at 194.2 nm. Atoms in the np $^{3}P$ excited states produce positive ions and electrons upon collisions with ${\mathrm{O}}_{2}$. In each case, Penning ionization and associative ionization are possible, and cannot be distinguished.Total rate constants for collisional ionization by ${\mathrm{O}}_{2}$ at room temperature are (2\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$for n=4 and (4\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$ for n=5. Einstein A coefficients are calculated for all allowed fluorescence transitions originating from the 4p $^{3}P$ and 5p $^{3}P$ electronic states. For each state, the sum of the calculated Einstein A coefficients agrees well with the experimental zero-pressure decay rate. Rate constants for collisional removal of population from these states by the background gas (which is mostly ${\mathrm{O}}_{2}$) are 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$ ${\mathrm{cm}}^{3}$${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$ for n=4 and 7.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$ for n=5. The photoionization cross section for atoms in the 4p $^{3}P$electronic state is (3\ifmmode\pm\else\textpm\fi{}2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$. For atoms in the 5p $^{3}P$ state the photoionization cross section is less than 1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}17}$ ${\mathrm{cm}}^{2}$.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTProton production in one- and two-color laser ionization and dissociation of molecular hydrogenJesse D. Buck, David H. Parker, and David W. ChandlerCite this: J. Phys. Chem. 1988, 92, 13, 3701–3705Publication Date (Print):June 1, 1988Publication History Published online1 May 2002Published inissue 1 June 1988https://pubs.acs.org/doi/10.1021/j100324a004https://doi.org/10.1021/j100324a004research-articleACS PublicationsRequest reuse permissionsArticle Views94Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

We have measured the two-photon cross section for the Q1 branch of the EF(v = 6) ← X(v = 0) transition in H2, using techniques developed in this laboratory. The population of the excited EF level was determined using a calibrated fluorescence detection system to monitor B(v = 1) ← EF(v = 6) fluorescence at ~750 nm. Ions resulting from absorption of a third photon were collected on parallel wire electrodes and amplified with a calibrated charge-sensitive preamplifier. The temporal and spatial profiles of the laser pulses were characterized with a fast photodiode and a linear pyroelectric array, respectively. The 100-μm resolution of the pyroelectric array and the necessity to avoid saturation both dictate the use of a gently focused beam geometry. Our results (4.3×10−47 cm4/s−1 and 1.6 × 10−18 cm2) are in reasonable agreement with previous experiments and calculations, and we are currently working to upgrade our accuracy.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDouble-resonance laser-ionization spectroscopy of molecular hydrogen in the region of the second dissociation limitDavid H. Parker, Jesse D. Buck, and David W. ChandlerCite this: J. Phys. Chem. 1987, 91, 8, 2035–2037Publication Date (Print):April 1, 1987Publication History Published online1 May 2002Published inissue 1 April 1987https://pubs.acs.org/doi/10.1021/j100292a011https://doi.org/10.1021/j100292a011research-articleACS PublicationsRequest reuse permissionsArticle Views41Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

We are engaged in experiments to probe highly excited autoionizing levels of atomic oxygen using a double-resonance laser ionization scheme. Oxygen atoms are prepared by subjecting O2 to a microwave discharge at a pressure of ~0.2 Torr. A pump laser provides 225.7-nm photons to populate the 3p levels by two-photon absorption, also ionizing a small fraction of the excited atoms by absorption of a third photon. A second probe laser delayed by ~10 ns is scanned over energies of interest, and the ion current enhancement is recorded. We have observed ion signals from the 3d′(3S°, 3P°, 3D°) autoionizing states at ~124,000 cm−1. Absolute ionization cross sections are obtained by reference to the known value of 5.3 × 10−19 cm2 for 225.7-nm photons. A variety of autoionizing line shapes are observed, and further work is in progress to identify the nature of this behavior. We are also measuring cross sections for nonresonant ionization as the probe laser is tuned through the ionization continuum. The continuum data are useful for guiding the development of accurate theoretical descriptions of the final state in the ionization process.