First spectroscopic investigation of the 4 d transition metal monocarbide MoC

Journal ArticleThe first optical spectroscopic investigation of MoC has revealed a complicated vibronic spectrum consisting of about 35 bands between 17 700 and 24 000 cm-1. Analysis has shown the ground state to be the ?=0+ spin?orbit component of a 3?- state that derives from a 10?211?25rr42d 2 configuration. The X 3?0-+ rotational constant for 98Mo12C was determined to be B0=0.553 640?0.000 055 cm-1, giving r0=1.687 719?0.000 084 ?. Consideration of spin-uncoupling effects in the X 3?- state requires that this value be revised to r0=1.6760 ?, which represents our best estimate of the true Mo?C bond length. Spectroscopic constants were also extracted for six other major isotopic modifications of MoC in this mass resolved experiment. All rotationally resolved transitions were found to originate from the ground state and terminate in electronic states with ?=1. An attempt is made to classify the observed transitions into band systems, to rationalize the complexity of the spectrum, and to understand the bonding from a molecular orbital point of view

Electronic spectroscopy and electronic structure of diatomic CrC

Journal ArticleOptical spectra of jet-cooled diatomic CrC have been recorded in the near infrared region using resonant two-photon ionization spectroscopy combined with mass-selective detection of the resulting ions. Several weak transitions have been observed, along with one relatively strong band near 842 nm. Rotational resolution and analysis of this band confirms that the ground state is of ??? symmetry. Ab initio calculations have been performed that demonstrate that the ground state is highly multiconfigurational in nature, with a leading configuration of 1??2??1rr?1?? for the ten valence electrons. From the rotational analysis of the 842 nm ????X ??? band, the derived spectroscopic constants of the ground and excited states for ??Cr??C are B0"=0.659 97 (49), ?0" =6.74(24), ?0"=?0.066(20), T0=11 870.7660(65), B'=0.608 29(39), ?'=7.11(24), and ?'=0.144(17) cm?1. Here and throughout this article, 1? error limits are reported in parentheses. These rotational constants may be inverted to provide the bond lengths in the ground and excited states, r0"=1.6188(6) ? and r'=1.6861(5) ?, respectively. Ab initio calculations show that the upper state is the third state of 3?? symmetry

Vibronic spectroscopy of unsaturated transition metal complexes: CrC?H, CrCh?, and NiCH?

Journal ArticleVibronically resolved resonant two-photon ionization and dispersed fluorescence spectra of the organometallic radicals CrC2H, CrCH3 , and NiCH3 are reported in the visible and near-infrared wavelength regions. For CrC2H, a complicated vibronic spectrum is found in the 11 100?13 300 cm-1 region, with a prominent vibrational progression having ?'e=426.52?0.84 cm-1, ?'ex'e 50.74?0.13 cm-1. Dispersed fluorescence reveals a v"=1 level of the ground state with ?G"1/2=470?20 m-1. These vibrational frequencies undoubtedly pertain to the Cr?C2H stretching mode. It is suggested that the spectrum corresponds to the A? 6?1+ ? X? 6?+ band system, with the CrC2H molecule being linear in both the ground and the excited state. The related CrCH3 molecule displays a vibronic spectrum in the 11 500?14 000 cm-1 region. The upper state of this system displays six sub-bands that are too closely spaced to be vibrational structure, but too widely separated to be K structure. It is suggested that the observed spectrum is a 6E?X? 6A1 band system, analogous to the well-known B 6II?X 6?+ band systems of CrF and CrCl. The ground state Cr?CH3 vibration is characterized by ?'e=52?17 cm-1 and ?'ex'e=7.9?6 cm-1. The spectrum of NiCH3 lies in the 16 100?17 400 cm-1 range and has ?"e=455.3?0.1 cm21 and ?"ex"e=6.60 ?0.03 cm-1. Dispersed fluorescence studies provide ground state vibrational constants of ?"e=565.8?1.6 cm-1 and ?"ex"e+1.7?3.0 cm-1. Again, these values correspond to the Ni?CH3 stretching motion

Resonant two-photon ionization spectroscopy of NiC

Journal ArticleA spectroscopic investigation of jet-cooled diatomic NiC has revealed a complex pattern of vibronic levels in the wave number range from 21 700 to 27 000 cm-1. Of the more than 50 vibronic bands observed, 31 have been rotationally resolved and analyzed. All are ?'=0+??"=0+ transitions, consistent with the calculated 1S1 ground state of this molecule. Through the observation of vibrational hot bands in the spectra, these measurements have established that ?"e=875.155 cm-1, ?exe=5.38 cm-1, Be=0.640 38(14) cm-1, ?e=0.004 44(36) cm-1, and re =1.6273(2) ? for 58Ni12C. Several possible electronic band systems are observed, but the identification of these is hampered by extensive perturbations among the excited states. The observation of long-lived vibronic states as far to the blue as 26 951 cm21 indicates that D0(NiC) >3.34 eV, and the ionization energy of NiC has been determined to fall in the range IE(NiC) =8.73?0.39 eV. A discussion of these results, in the context of work on other 3d transition metal carbides is also presented

Optical spectroscopy of jet-cooled FeC between 12 000 and 18 100 cm-?

Journal ArticleIron monocarbide has been investigated between 12 000 and 18 100 cm21 in a supersonic expansion by resonant two-photon ionization spectroscopy. Six new electronic states have been identified for which origins relative to the ground state have been determined. Three of these possess ?"=3, one possesses ?'=4, and two possess ?'=2. The ?'=3 state with an origin near 13 168 cm-1 is likely a 3?3 state and has been assigned as the analog of the [14.0]??+ ?X??+ charge transfer transition in CoC. The ?'=4 state is most likely a 3?4 state. Additionally, seven bands with ?'=2 have been observed that have proven impossible to systematically group by electronic state. Because every transition rotationally resolved in this study possesses a lower state with ?=3, the ground state has been confirmed as arising from an ?=3 state that is most likely the ?=3 spin orbit component of a 3?i term derived from a 1?39?1 configuration. The ionization energy (IE) of FeC+ has been determined as 7.74?0.09 eV by varying the wavelength of the ionization photon. When combined with the known IE of Fe and the bond energy of FeC1, the bond energy of FeC is calculated to be 3.9?0.3 eV. Presentation of the results is accompanied by an analysis of the bonding in FeC from a molecular orbital standpoint

Resonant two-photon ionization spectroscopy of the 13-electron triatomic Si2N

ManuscriptResonant two-photon ionization spectra of 28Si2N, 28,29Si2N, and 28,30Si2N have been collected between 32 000 cm-1 and 36 000 cm-1. A fit of the rotationally resolved spectrum of the most intense band of 28Si2N at 34 314 cm-1 reveals the transition to be 2?+u ? X~ 2IIg,1/2- A molecular orbital analysis is made to justify the assignment. The geometric structure is determined to be linear and centrosymmetric in both the ground and excited state with r0 O(Si-N) = 1.6395 ? 0.0014 ? and rN(Si-N) = 1.6343 ? 0.0014 ?. The ionization energy is determined to be less than 8.51 eV

Hollywood Free Paper, October 19 1971

https://digitalcommons.fuller.edu/hollywoodfreepaper/1051/thumbnail.jp

Household Responses to Pandemic (H1N1) 2009–related School Closures, Perth, Western Australia

Results from closures will determine the appropriateness and efficacy of this mitigation measure

Hemolytic Uremic Syndrome Risk and Escherichia coli O157:H7

We reviewed medical records of 238 hospitalized patients with Escherichia coli O157:H7 diarrhea to identify risk factors for progression to diarrhea-associated hemolytic uremic syndrome (HUS). Data indicated that young age, long duration of diarrhea, elevated leukocyte count, and proteinuria were associated with HUS