131 research outputs found
RE-ANALYSIS OF THE DISPERSED FLUORESCENCE SPECTRA OF THE C3-RARE GAS ATOM COMPLEXES
Get PDFThe dispersed fluorescence (DF) spectra of the CNe, CAr, CKr, and CXe complexes near the 0 2 0- 000, 0 4 0- 000, 0 2 0- 000 and 100-000 bands of the ~{A}-~{X}
system of Cfootnote{G. Zhang, B.-G. Lin, S.-M. Wen, and Y.-C. Hsu, J. Chem. Phys. {bf120}, 3189(2004); J.-M. Chao, K. S. Tham, G. Zhang, A. J. Merer, Y.-C. Hsu, and W.-P. Hu, J. Chem. Phys. {bf134}, 074313(2011)} have been revisited. Some of the DF spectra of the Ne and Ar complexes have been recently obtained with a slightly improved resolution of 6-10 wn. All the DF spectra have been reassigned as emission from van der Waals (vdW) complexes and C fragments. The optically excited C-Rg (Rg = rare-gas atom) complexes fluorescence and/or decay down to slightly lower (about 2-30 wn) vibrational levels without changing the internal energy of C and then predissociate via the continua of the nearby vibronic states of C. The available dissociation channels depend on the binding energy of the ground electronic state complex. Exceptions have been found at the vdW bands near the 0 4 0- 000 band of C. The binding energies of the ground electronic states of these four complexes will be discussed.Made available in DSpace on 2016-01-05T20:02:28Z (GMT). No. of bitstreams: 3
1084.pdf: 19979 bytes, checksum: d36d62c2244948352033ccdcff1552af (MD5)
397828.pptx: 2850981 bytes, checksum: 0efb6951ae15eb90d4c286da717cb480 (MD5)
license.txt: 4813 bytes, checksum: 715c4321821a960fa1a1e91d2ac7ebce (MD5)
Previous issue date: 2
Spectroscopic characterization of isomerization transition states
Get PDFTransition state theory is central to our understanding of chemical reaction dynamics. We demonstrate here a method for extracting transition state energies and properties from a characteristic pattern found in frequency domain spectra of isomerizing systems. This pattern, a dip in the spacings of certain barrier-proximal vibrational levels, can be understood using the concept of effective frequency, . The method is applied to the \textit{cis}-\textit{trans} conformational change in the S state of CH and the bond-breaking HCN-HNC isomerization. In both cases, the barrier heights derived from spectroscopic data agree extremely well with previous \textit{ab initio} calculations. We also show that it is possible to distinguish between vibrational modes that are actively involved in the isomerization process and those that are passive bystanders. (This work has been published in J.~H.~Baraban, P.~B.~Changala, G.~Ch.~Mellau, J.~F.~Stanton, A.~J.~Merer, and R.~W.~Field. Spectroscopic characterization of isomerization transition states. {\em Science}, 350(6266):1338--1342, 2015.)Made available in DSpace on 2017-01-26T21:39:48Z (GMT). No. of bitstreams: 3
license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5)
1674.pdf: 18855 bytes, checksum: af4ab9a1f10080e4a2240f273ac3034a (MD5)
614358.pptx: 9094129 bytes, checksum: e8621278785d8ccae5c3438eb77bb09c (MD5)
Previous issue date: 2016-06-2
DOPPLER-LIMITED DYE LASER EXCITATION SPECTROSCOPY OF HCCL: THE VIBRONIC BAND
No full textA. J. Merer and D. N. Travis, Can. J. Phys. 44 525 (1966)Author Institution: Herzberg Institute of Astrophysics, National Research Council of CanadaThe chloromethylene radical, HCCl, was first observed in the gas phase by Merer and . They found that the molecule in the excited state is ``straightened” by vibration and that the (010) level is below the barrier to linearity. The (010)-(000) band around has been observed with Doppler - limited resolution of using a CW dye laser. The HCCl molecule was generated by a reaction of discharged with . A rotational analysis will be presented
INVISIBLE ELECTRONIC STATES AND THEIR DYNAMICS REVEALED BY PERTURBATIONS
No full textAuthor Institution: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei; TaiwanSooner or later everyone working in the field of spectroscopy encounters perturbations. These can range in size from a small shift of a single rotational level to total destruction of the vibrational and rotational patterns of an electronic state. To some workers perturbations are a source of terror, but to others they are the most fascinating features of molecular spectra, because they give information about molecular dynamics, and about states that would otherwise be invisible as a result of unfavorable selection rules. An example of the latter is the essentially complete characterization of the \tilde{b}A state of SO from the vibronic perturbations it causes in the \tilde{a}B state. The S-trans state of acetylene is a beautiful example of dynamics in action. The level patterns of the three bending vibrations change dramatically with increasing vibrational excitation as a result of the vibrational angular momentum and the approach to the isomerization barrier. Several vibrational levels of the S-cis isomer, previously thought to be unobservable, can now be assigned. They obtain their intensity through interactions with nearby levels of the trans isomer
Development of a new detection scheme to probe predissociated levels of the S1 state of acetylene
Get PDFA new spectroscopic scheme has been developed to probe the predissociated levels of the S state of acetylene. Our new scheme is based on detection of visible fluorescence that is a result of multi-photon excitation of acetylene (resonantly through single rovibronic S levels). The new detection scheme is not subject to decreases in fluorescence quantum yield of S levels that lie above the predissociation limit, and laser scatter-light can be easily eliminated by a long-pass filter with a cutoff in the visible range. For the S predissociated levels, the new detection scheme offers much improved signal-to-noise ratio compared to the conventional laser-induced fluorescence technique, based on detection of UV fluorescence from the S levels. The new method is also easier to implement than various H-atom detection schemes, which involve one additional laser of different wavelength than the excitation wavelength. Based on the power dependence and lifetime of the fluorescence signals, electronically excited \chem{C_2H} and/or \chem{C_2} fragments are the likely emitters of the detected visible fluorescence. The new method is currently being used to extend the vibrational and rotational assignments of both gerade and ungerade levels of the S state of acetylene in the region of the - isomerization barrier, 1000 cm above the onset of S predissociation.Made available in DSpace on 2017-01-26T21:38:39Z (GMT). No. of bitstreams: 3
license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5)
1867.pdf: 19707 bytes, checksum: d95e608e84f93bb4d4d040296fefc661 (MD5)
685189.pptx: 467348 bytes, checksum: 059ae3279bce79f63e06a28f3aef28bb (MD5)
Previous issue date: 2016-06-2
The low-lying electronic states of scandium monocarbide, ScC
Get PDFMade available in DSpace on 2017-07-27T20:15:59Z (GMT). No. of bitstreams: 2
2367.pdf: 21023 bytes, checksum: a48c92872dd1b4174cc1b92639ccf2a6 (MD5)
license.txt: 4814 bytes, checksum: a3dad671d2baf2db10a2bec0f2e0c408 (MD5)
Previous issue date: 6Made available in DSpace on 2018-01-29T23:02:27Z (GMT). No. of bitstreams: 3
license.txt: 4814 bytes, checksum: a3dad671d2baf2db10a2bec0f2e0c408 (MD5)
2367.pdf: 21023 bytes, checksum: a48c92872dd1b4174cc1b92639ccf2a6 (MD5)
868689.pptx: 2995727 bytes, checksum: 735106de2e676ca027f72c30038fb682 (MD5)
Previous issue date: 6Extensive wavelength-resolved fluorescence studies have been carried out for the electronic bands of ScC and ScC lying in the range 14000 - 16000 cm. Taken together with detailed rotational analyses of these bands, these studies have clarified the natures of the low-lying electronic states. The ground state is an = 3/2 state, with a vibrational frequency of 648 cm, and the first excited electronic state is an = 5/2 state, with a frequency of 712 cm, lying 155.54 cm higher. These states are assigned as the lowest spin-orbit components of X and a, respectively. The quartet nature of the a state is confirmed by the observation of the component, 18.71 cm above the component. The strongest bands in the region studied are two - transitions, where the upper states lie 14355 and 15445 cm above X. Extensive doublet-quartet mixing occurs, which results in some complicated emission patterns. The energy order, a above X, is consistent with the ab initio calculations of Kalemos et al.,footnote{ A. Kalemos, A. Mavridis and J.F. Harrison, J. Phys. Chem. {bf A155}, 755 (2001).} but differs from that found by Simard et al in the isoelectronic YC molecule.footnote{B. Simard, P.A. Hackett and W.J. Balfour, Chem. Phys. Lett., {bf 230}, 103 (1994).
MOLECULAR BEAM OPTICAL STARK SPECTROSCOPY OF SiCH AND GeCH
No full textT. C. Smith, H. Li, D. J. Clouthier, C. T. Kingston and A. J. Merer, J. Chem. Phys. 112, 3662 (2000). T. C. Smith, H. Li, D. J. Clouthier, C. T. Kingston and A. J. Merer, J. Chem. Phys. 12, 8417 (2000).Author Institution: University of Kentucky; Department of Chemistry, University of Kentucky; Department of Chemistry, Arizona State UniversityLaser-induced fluorescence spectra of selected features of the band systems of the SiCH and GeCH radicals have been recorded at sub-Doppler resolution. As in previous the radicals were produced in a pulsed discharge jet source using methyltrichlorosilane and methyltrichlorogermane as precursors. With linewidths of 35 MHz, the proton magnetic hyperfine splittings have been resolved and the upper state Fermi contact parameter determined. In addition, optical Stark experiments were performed to measure the ground and excited state permanent electric dipole moments. The analysis of the Stark and hyperfine data will be presented and the derived parameters will be discussed
THE VACUUM ULTRAVIOLET ABSORPTION SPECTRUM OF DIAZOMETHANE
No full textAuthor Institution: Division of Pure Physics, National Research CouncilUltraviolet absorption spectra of and between 2000 {\AA} and 1350 {\AA} have been photographed. Many electronic transitions occur in this region, including a Rydberg series (first reported by Herzberg) which gives the first I.P. of diazomethane as eV. Examination of a band system at 1900 {\AA} has shown that it contains three close-lying electronic transitions, with origins within . Of the upper states, the two outermost, D and F, are shown by rotational analysis to be of the same symmetry species , while the third, E, lying between them, seems to be responsible for large perturbations observed in the K-structures. By inference, this third state must be , in Coriolis interaction with the two states. Various vibrational bands of this 1900 {\AA} group have been assigned; among these are a number of vibrationally-forbidden bands involving one and three quanta of the out-of-plane bending frequency, . There is strong evidence that the molecule remains planar in these excited states
EXTENDED PERMUTATION-INVERSION GROUPS FOR SIMULTANEOUS TREATMENT OF THE ROVIBRONIC STATES OF TRANS-ACETYLENE, CIS-ACETYLENE, AND VINYLIDENE
No full textAuthor Institution: Optical Technology Division, NIST, Gaithersburg, MD 20899-8441, MD, USA; Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan 10617 and Department of Chemistry, University of British Columbia, Vancouver, B.C., Canada V6T 1Z1The electronic ground state potential surface of acetylene (HCCH) has a minimum at the linear conformation, but the excited electronic states may have potential minima at a variety of nonlinear equilibrium shapes. This work is concerned with the group theoretical ideas necessary to treat simultaneously the symmetry properties of rovibronic states associated with three different planar acetylene equilibrium configurations, namely trans bent acetylene, cis bent acetylene, and vinylidene (H2C=C). We make use of three different kinds of groups: (i) point groups, (ii) permutation-inversion (PI) groups, and (iii) extended PI groups. The PI group is G or G, depending on whether C-H bond breaking is impossible (no bent acetylene vinylidene interconversion), or possible. The extended PI groups are G and G, respectively, when the only large amplitude motions are the CCH bends at each end of the molecule, and G and G, respectively, when internal rotation is added as a third large amplitude motion. Applied to acetylene, the results indicate that there will be no splittings of the rovibronic levels unless CH bond breaking occurs. Even without bond breaking, however, states of the cis and trans isomers just below their interconversion barrier will show "staggerings" in their -structures, i.e., a given vibrational level will have three tunneling components at slightly different energies: one component will have levels with only (where is an integer), a second component will have levels with only, and the third will have only odd- levels. New experimental results for the S-cis electronic state of acetylene are reviewed, and are found to be consistent with the group theory in so far as comparison is possible
ROTATIONAL STRUCTURE IN SOME HIGHER ELECTRONIC STATES OF GeF
No full text R. F. Barrow, D. Butler, J.W.C. Johns, and J. L. Powell, 1959 Proc. Phys. Soc. 73, 317; A. N. Uzikov and Yu. Ya. Kuzyakov. 1969 Vestn. Mosk. Univ. 11 (Khim) 24, 30.Author Institution: Department of Chemistry, University of British ColumbiaFrom analysis of the rotational structure in several emission transitions involving higher electronic states of , molecular constants have been derived for four additional excited states. These are the and states (previously known from lower dispersion ), and two new Rydberg states, and , which form a complex near 50
- …
