@article {2260, title = {Direct observation of the symmetric stretching modes of (A)over-tilde(1) A(u) acetylene by pulsed supersonic jet laser induced fluorescence}, journal = {Molecular Physics}, volume = {106}, number = {15}, year = {2008}, note = {ISI Document Delivery No.: 371LATimes Cited: 1Cited Reference Count: 24Steeves, Adam H. Merer, Anthony J. Bechtel, Hans A. Beck, Annelise R. Field, Robert W.}, pages = {1867-1877}, type = {Article}, abstract = {Rotational analyses are reported for the 2(0)(2) and 1(0)(1) bands of the (A) over tilde (1) A(u) <- (X) over tilde (1) Sigma(+)(g) transition of C2H2 near 45,000 cm(-1) (+2800 cm(-1) relative to T-0) from jet-cooled laser-induced fluorescence spectra. While the 220 band is unperturbed and straightforward to assign, the 1(1) level is strongly perturbed by interactions with the 2(1) B-2 polyad, where upsilon B{\textquoteright} = upsilon(4){\textquoteright} + upsilon(6){\textquoteright}. In order to assign the lines of this band, a population-labelling technique was used, employing an infrared laser to deplete the population in selected ground state rotational levels before probing with the ultraviolet laser. Deperturbation of the 1(1)/2(1) B-2 interaction leads to the value v(1){\textquoteright} = 2880.08 cm(-1) for the fundamental symmetric C-H stretching frequency. Assignments are also reported for the 2 3 and 1 1 2 1 levels, completing all assignments of levels containing excitation in only the totally symmetric vibrational modes up to + 4500 cm(-1). The reassignment of upsilon(1){\textquoteright} implies that some of currently accepted assignments above 47,000 cm(-1) are in error and suggests that the interpretation of some aspects of the near-threshold photodissociation measurements of Mordaunt et al. [J. Chem. Phys. 108, 519 (1998)] may need to be revisited.}, keywords = {AB-INITIO MO, acetylene, ASSIGNMENT, C2H2, DEPERTURBATION, excited states, PARTIAL, PHOTODISSOCIATION, S-1((1)A(U)) STATE, SPECTROSCOPY, vibration-rotation analysis, VIBRATION-ROTATION CONSTANTS, vibrational spectroscopy, WAVELENGTH BANDS, X BAND SYSTEM}, isbn = {0026-8976}, url = {://000260831600004}, author = {Steeves, A. H. and Merer, A. J. and Bechtel, H. A. and Beck, A. R. and Field, R. W.} } @article {2328, title = {Observation of above-threshold dissociation of Na-2(+) in intense laser fields}, journal = {Physical Review A}, volume = {78}, number = {2}, year = {2008}, note = {ISI Document Delivery No.: 349EFTimes Cited: 0Cited Reference Count: 21Zhang, Qun Hepburn, John W. Shapiro, MoshePart A}, month = {Aug}, pages = {4}, type = {Article}, abstract = {We report the observation of above-threshold dissociation of a multielectron molecular system, Na-2(+). The process is due to continuum-continuum transitions in a field-dressed molecular continuum. Three well-resolved fragmentation channels with different kinetic energy release patterns have been detected, of which two are associated with ordinary photodissociation via "light-induced potentials" into Na(3s)+Na+ and Na(3p)+Na+, and one with continuum-continuum transitions and above-threshold dissociation into Na(3p)+Na+. We show that when we dress this molecule with a field whose intensity is similar to 3 X 10(12) W/cm(2), above-threshold dissociation prevails over other processes, such as field ionization followed by Coulomb explosion.}, keywords = {D-2, DYNAMICS, FEMTOSECOND, H-2(+), H2, MOLECULES, MULTIPHOTON IONIZATION, PHOTODISSOCIATION}, isbn = {1050-2947}, url = {://000259263400012}, author = {Zhang, Q. and Hepburn, J. W. and Shapiro,Moshe} } @article {1417, title = {Threshold ion-pair production spectroscopy of HCN}, journal = {Journal of Chemical Physics}, volume = {124}, number = {7}, year = {2006}, note = {ISI Document Delivery No.: 014IPTimes Cited: 4Cited Reference Count: 32}, month = {Feb}, pages = {5}, type = {Article}, abstract = {The spectroscopic technique of threshold ion-pair production spectroscopy (TIPPS) has been applied to the triatomic molecule HCN. We have recorded the total ion-pair yield and TIPP spectra for the HCN -> H++CN- process using coherent vacuum ultraviolet excitation. From the simulation of our high-resolution TIPP spectrum we have precisely measured the HCN ion-pair threshold E-IP(0) to be 122 244 +/- 4 cm(-1). This value could be used to determine the bond dissociation energy D-0(H-CN) to unprecedented accuracy. Our fitting result also showed that rotationally excited instead of cold CN- fragment is favored as the ion-pair dissociation product in the threshold region.}, keywords = {CN, DCN, DYNAMICS, ELECTRONIC STATES, MOLECULE, NM, PHOTO-DISSOCIATION, PHOTODISSOCIATION, PHOTOIONIZATION, TIPPS}, isbn = {0021-9606}, url = {://000235473500018}, author = {Hu, Q. J. and Zhang, Q. and Hepburn, J. W.} } @article {723, title = {Resonance enhanced multiphoton dissociation of polycyclic aromatic hydrocarbons cations in an RF ion trap}, journal = {Chemical Physics Letters}, volume = {373}, number = {3-4}, year = {2003}, note = {ISI Document Delivery No.: 681BGTimes Cited: 7Cited Reference Count: 35}, month = {May}, pages = {292-298}, type = {Article}, abstract = {We present a novel method for recording the absorption spectra of cations of non-volatile molecules using resonance enhanced multiphoton dissociation of trapped ions. Ions are produced through a 2-1aser desorption/ionization process in an RF ion trap mass-spectrometer. A third tunable visible laser induces fragmentation of the trapped ions with a yield dependent on the absorption cross-sections of the ions. Using this method we have recorded the visible absorption spectrum of two PAH isomers, phenanthrene and anthracene. (C) 2003 Elsevier Science B.V. All rights reserved.}, keywords = {ENERGETICS, fragmentation, GAS-PHASE, IONIZATION, IR EMISSION, MASS-SPECTROMETRY, PAHs, PHOTODISSOCIATION, RADICAL CATIONS, SPECTROSCOPY}, isbn = {0009-2614}, url = {://000183016300010}, author = {Rolland, D. and Specht, A. A. and Blades, M. W. and Hepburn, J. W.} } @article {4417, title = {A semiclassical approach to intense-field above-threshold dissociation in the long wavelength limit. II. Conservation principles and coherence in surface hopping}, journal = {Journal of Chemical Physics}, volume = {109}, number = {14}, year = {1998}, note = {ISI Document Delivery No.: 125BETimes Cited: 28Cited Reference Count: 24}, month = {Oct}, pages = {5747-5760}, type = {Article}, abstract = {This paper is a companion to our recently published semiclassical formalism for treating time-dependent Hamiltonians [J. Chem. Phys, 105, 4094 (1996)], which was applied to study the dissociation of diatomic ions in intense laser fields. Here two fundamental issues concerning this formalism are discussed in depth: conservation principles and coherence. For time-dependent Hamiltonians, the conservation principle to apply during a trajectory hop depends upon the physical origin of the electronic transition, with total energy conservation and nuclear momentum conservation representing the two limiting cases. It is shown that a]applying an inappropriate scheme leads to unphysical features in the kinetic energy of the dissociation products. A method is introduced that smoothly bridges the two limiting cases and applies the physically justified conservation scheme at all times. It is also shown that the semiclassical formalism can predict erroneous results if the electronic amplitudes for well-separated hops are added coherently. This is a fundamental problem with the formalism which leads to unphysical results if left unattended. Alternative schemes are introduced for dealing with this problem and their accuracies are assessed. Generalization of the well-known Landau-Zener formula to the time-dependent Hamiltonian case is derived, which allows one to significantly decrease the computational overhead involved with the numerical implementation of the semiclassical method. Finally, we show that in strong-field molecular dissociation a trajectory can {\textquoteright}{\textquoteright}surf" a moving avoided crossing. In this case the hopping probability is a sensitive function of the interference between two closely spaced avoided crossing regions. (C) 1998 American Institute of Physics.}, keywords = {COULOMB EXPLOSION, DIATOMIC-MOLECULES, ENHANCED, H-2(+), IONIZATION, LASER FIELDS, MODEL, MOLECULAR-DYNAMICS, PHOTODISSOCIATION, QUANTUM DECOHERENCE, TRANSITIONS}, isbn = {0021-9606}, url = {://000076216900008}, author = {Thachuk, M. and Ivanov, M. Y. and Wardlaw, D. M.} }