TRANSIENT FREQUENCY MODULATION SPECTROSCOPY OF TRANSITON METAL CONTAINING MOLECULES

Author Institution: Department of Chemistry and Biochemistry, Arizona State UniversityTransient frequency modulation (TFM) spectroscopy is an attractive spectroscopic technique because of its intrinsic high spectral resolution and its match with our pulsed molecular beam generation schemes. A progress report will be given on the construction of the TFM spectrometer and its application to the detection and characterization of transition metal radicals in the visible and near infrared region. Absorption based spectroscopy is desired due to the low fluorescence quantum yield of many species and the low detector sensitivity of GaAs photomultiplier tubes currently used

OPTICAL STARK SPECTROSCOPY OF MOLYBDENUM CARBIDE, MoC

{I. Shim and K. A. Gingerich \textit{J. Chem. Phys.Author Institution: Department of Chemistry and Biochemistry,; Arizona State University, Tempe, AZ 85287-1604High resolution optical spectroscopy has been used to study a molecular beam of molybdenum carbide, MoC. The R_{e}(0) (\nu=18612.978 \wn) and Q_{fe}(1) (\nu=18611.872 \wn) branch features of the (0,0) $[18.6]^{3}\Pi_{1}-X^{3}\Sigma^{-}$ system of $^{98}MoC$ were analyzed using Stark spectroscopy. Electric field induced splitting in the laser induced fluorescence (LIF) spectra was analyzed to measure permanent electric dipole moments of 2.69(2)D and 6.32(20)D for the $[18.6]^{3}\Pi_{1}$ and $X^{3}\Sigma^{-}$ states, respectively. Excited state hyperfine structure has been observed for the first time in $^{95}MoC$ and $^{97}MoC$. Experimental results will be compared to theoretical predictions, } \underline{\textbf{106}}, 8093 (1997).} and the electronic structure will be discussed using a molecular orbital correlation model. The MoC dipole moments will be compared with those of other transition metal monocarbides. An interesting observation is that the \textit{ab initio} calculations for second row transition metal monocarbides are more reliable than predictions for the first row carbides

THE PERMANENT ELECTRIC DIPOLE MOMENTS AND MAGNETIC HYPERFINE INTERACTON IN THE A2ΠA^{2}\Pi STATE OF YTTRIUM MONOSULFIDE, YS

Author Institution: Department of Chemistry and Biochemistry, Arizona State UniversityThe optical Stark effect in the $(0,0) A^{2}\Pi - X^{2}\Sigma^{+}$ band systems of a yttrium monosulfide, YS , supersonic molecular beam sample have been analyzed to produce permanent electric dipole moments, $\mu$, for the $A^{2}\Pi_{3/2}$, and $A^{2}\Pi_{1/2}$ states of $5.9(2) D$, and $6.8(1) D$, respectively. Fine structure splitting in the field free $A^{2}\Pi_{3/2} - X^{2}\Sigma^{+}$ and $A^{2}\Pi_{1/2} - X^{2}\Sigma^{+}$ spectra were analyzed to produce the magnetic hyperfine spectroscopic parameters $a = -36(6)$ MHz, $c = 111(7)$ MHz, and $d = -107(6)$ MHz for the $A^{2}\Pi$ state. Transition frequencies of the low rotational lines in the $(0,0) A^{2}\Pi_{r} - X^{2}\Sigma^{+}$ band system were measured and analyzed to produce the first complete set of fine structure parameters for the $A^{2}\Pi_{r}$ state

THE PERMANENT ELECTRIC DIPOLE MOMENTS FOR THE A2ΠA^{2}\Pi AND B2Σ+B^{2}\Sigma^{+} STATES AND THE HYPERFINE INTERACTIONS IN THE A2ΠA^{2}\Pi STATE OF LANTHANUM MONOXIDE

1. R.F. Seunram, F.J. Lovas, G.T. Fraser and K. Matsumura, J. Chem. Phys. 92, 4724 (1990).Author Institution: Department of Chemistry and Biochemistry, Arizona State UniversityThe optical Stark effect in the $(0,0) A^{2}\Pi_{3/2} - X^{2}\Sigma^{+}, A^{2}\Pi_{1/2} - X^{2}\Sigma^{+}$ and $B^{2}\Sigma^{+} - X^{2}\Sigma^{+}$ band systems of a lanthanum monoxide, LaO, supersonic molecular beam sample have been analyzed to produce permanent electric dipole moments, $\mu$, for the $A^{2}\Pi_{3/2}, A^{2}\Pi_{1/2}$ and $B^{2}\Sigma^{+}$ states of 1.89(6)D, 2.44(2)D and 0.2(1)D, respectively. The ground state dipole moment was determined some time $ago^{1}$ to be 3.207(11)D. Fine structure splitting in the field free $A^{2}\Pi_{3/2} - X^{2}\Sigma^{+}$ and $A^{2}\Pi_{1/2} - X^{2}\Sigma^{+}$ spectra was analyzed to produce the magnetic hyperfine spectroscopic parameters a = 233(4) MHz, c = -261(12) MHz, and d = 410(4) MHz. The Group IIIA monoxides, ScO, YO and LaO are prototypical examples of transition metal-oxide bonded molecules. This work on LaO has resulted in the first complete set of dipole moment measurements for the $X^{2}\Sigma^{+}, A^{2}\Pi_{1/2}, A^{2}\Pi_{3/2}$ and $B^{2}\Sigma^{+}$ states for any of these monoxides. The permanent electric dipole moments for the low-lying states of LaO are exceedingly small, given that they are conventionally viewed as having a $La^{+2}O^{-2}$ charge distribution and exhibiting a large variation amongst the four states

SPECTRA AND DYNAMICS OF MOLECULES IN LONG-LIVED, HIGHLY REACTIVE TRIPLET STATES

Author Institution: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139Molecules in their excited triplet states are highly chemically reactive. They are metastable, with long radiative lifetimes $( > 100\mu s)$, carry chemically significant energy $( > 50 kcal/mol)$, and can exist in several isomeric forms. These characteristics make molecules in triplet states act as chemical protagonists in reactions initiated by ultraviolet radiation, and in energetic environments where collisions are the reaction initiators. Despite their key role in chemical reactions, molecules in triplet states can easily elude detection, largely because they do not make their presence known via fluorescence. The excitation and de-excitation dynamics of triplet states is not well understood. As an alternative to direct optical pumping, excitation transfer from a metastable atom to a target organic molecule for selective, efficient population of triplet states is very promising. In this scheme, a donor atom is optically excited via a two-photon transition, and the excitation energy is transferred from the atom to the acceptor molecule in a pulsed jet expansion. Hg atoms are used in this indirect, collision-induced photosensitized excitation transfer experiment to populate the metastable triplet states of target molecules such as acetylene and ethylene. SEELEM (surface electron ejection by laser excited metastables) is the detection method for both the laser excited atomic species and the product metastable molecules. SEELEM is employed as a probe of triplet state excitation and de-excitation dynamics. A double-resonance 'SEELEM dip' experiment will be described in which one of the metastable species is selectively depopulated via laser. The goal is characterization of the molecular triplet states, leading to illumination of the dynamical processes which underlie their complex spectra

THE PERMANENT ELECTRIC DIPOLE MOMENTS OF THE X3Δ,E3Π,A3ΦX^{3} \Delta, E^{3}\Pi, A^{3}\Phi AND B3ΠB^{3}\Pi STATES OF TITANIUM MONOXIDE, TiO

Author Institution: Department of Chemistry and Biochemistry, Arizona State University; Chemistry Department, Brookhaven National LaboratoryThe optical Stark spectrum of the origin bands of the $E^{3}\Pi_{0} - X^{3}\Delta_{1}, A^{3}\Phi_{2} - X^{3}\Delta_{1}$, and $B^{3}\Pi_{0} - X^{3}\Delta_{1}$ band systems of titanium monoxide, TiO, were analyzed to produce permanent electric dipole moments of $3.34(1)D, 3.2(4)D, 4.89(5)D$ and $4.9(2)D$ for the $X^{3}\Delta_{1}, E^{3}\Pi_{0}, A^{3}\Phi_{2}$ and $B^{3}\Pi_{0}$ states, respectively. The observations are compared with a simple molecular orbital description for the low-lying states and electronic structure calculations