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The unimolecular photodissociation dynamics of acetone spanning the entire S1 ← S0 absorption spectrum have been reinvestigated, with a focus on mechanisms that produce CO. At excitation wavelengths of λ > 305.8 nm, all photoproducts are formed on the S0 state after internal conversion. A roaming mechanism forming C2H6 + CO is active in the window λ = 311.2–305.8 nm. From λ = 305.8 to 262 nm, little or no CO is produced with the photochemistry dominated by the Norrish-type I C–C bond cleavage on the lowest excited triplet state, T1. At higher energy (λ < 262 nm), an increasing fraction of CH3CO radicals from the primary reaction have sufficient internal energy to spontaneously decompose to CH3 + CO. A new model is presented to account for the kinetic energy distribution of the secondary CH3 radical, allowing us to determine the height of the energetic barrier to CH3CO decomposition as 68 ± 4 kJ mol−1, which lies midway between previous measurements. The fraction of CO from triple fragmentation rises smoothly from 260 to 248 nm. We see no evidence of the return of roaming, or any other S0 reaction, in this higher energy region of the first electronic absorption band. [ABSTRACT FROM AUTHOR]

The 3³Πgg state of the dicarbon molecule, C2, has been identified for the first time by a combination of resonant ionization spectroscopy, mass spectrometry, and high-level ab initio quantum chemical calculations. This marks the discovery of the final valence triplet state of C2 spectroscopically accessible from the lowest triplet state. It is found to be vibronically coupled to the recently discovered 4³Πgg state, necessitating vibronic calculations beyond the Born-Oppenheimer approximation to reconcile calculated rotational constants with observations. The 3³Πgg state of C2 is observed to have a much shorter fluorescence lifetime than expected, possibly pointing to predissociation by coupling to the unbound d³Πgg state. [ABSTRACT FROM AUTHOR]

Resonant two-photon threshold ionization spectroscopy is employed to determine the ionizationenergy of C2 to 5 meV precision, about two orders of magnitude more precise than the previously accepted value. Through exploration of the ionization threshold after pumping the 0-3 band of the newly discovered 4³Πg←a³Πu band system of C2, the ionizationenergy of the lowest rovibronic level of the a³Πu state was determined to be 11.791(5) eV. Accounting for spin-orbit and rotational effects, we calculate that the ionizationenergy of the forbidden origin of the a³Πu state is 11.790(5) eV, in excellent agreement with quantum thermochemical calculations which give 11.788(10) eV. The experimentally derived ionizationenergy of X¹Σg+X¹Σg+ state C2 is 11.866(5) eV. [ABSTRACT FROM AUTHOR]

Infrared spectra are reported for the N[sub 2]-HF and OC-HF complexes formed in helium nanodroplets. The spectra are rotationally resolved and show that the structures of the complexes are essentially the same (linear) as determined previously from gas phase studies. The rotational constants of the helium solvated complexes are smaller than the gas phase values, in agreement with what has been previously observed for several other systems. N[sub 2]- HF is particularly interesting when studied in the presence of a large electric field, given that the change in the dipole moment upon vibrational excitation is large, so that the individual transitions in the pendular spectrum can be resolved. This enables us to monitor the change in the helium environment around the molecule as it goes from rotational to pendular motion. The results also reveal that the relaxation lifetime of these pendular states in helium is comparable to the flight time of the droplets through the electric field and depends upon the droplet size. [ABSTRACT FROM AUTHOR]

Rotationally resolved spectra of h[sub 2]- and d[sub 1]-formic acid embedded in liquid helium droplets have been recorded in the spectral region of the O–H (ν[sub 1]) and C–H (ν[sub 2]) stretch vibrations. Accidental resonant mixing between the ν[sub 1]-band of h[sub 2]-formic acid and the combination bands (ν[sub 2]+ν[sub 7]) and (ν[sub 2]+ν[sub 9]) has been observed. The fundamental ν[sub 1] band can interact via Fermi resonance with the (ν[sub 2]+ν[sub 7]), and the (ν[sub 2]+ν[sub 7]) via Coriolis coupling with the (ν[sub 2]+ν[sub 9]) band. Examination of the resonance induced line-broadening effects suggests that the helium environment modifies vibrational relaxation dynamics. The 2ν[sub 3] C==O stretch overtone is also observed and was assigned by a density functional theory (DFT) ab initio calculation. The spectroscopic constants are determined by fitting all spectra with a standard gas phase Hamiltonian. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Infrared spectra are reported for Ar[sub n]–HF complexes up to the closing of the first solvent shell. These complexes were grown in superfluid helium droplets, leading to the formation of multiple isomers for n>3. The vibrational frequency shifts associated with the HF stretch are in excellent agreement with previous theoretical calculations. The relative abundances of the various isomers is found to be dependent upon the order of pick-up of the HF and argon. When HF is added to the droplets first the isomers corresponding to the solvated HF are produced in high abundance. Growth of the argon cluster prior to addition of the HF leads to the latter being on the “surface” of the argon cluster. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Infrared spectra are reported for carbon dioxide and nitrous oxide solvated in superfluid helium droplets, corresponding to the vibrational excitation of the (02[sup 0]1)/(10[sup 0]1) Fermi diad. Although the rotational constants of these two molecules are similar in the gas phase, they are observed to be quite different in liquid helium, namely, 0.154 cm[sup -1] for CO[sub 2] and 0.0717 cm[sup -1] for N[sub 2]O. In addition, solvation in helium results in shifts in the vibrational origin that are in the opposite directions, -0.42 cm[sup -1], for CO[sub 2] and +1.2 cm[sup -1] for N[sub 2]O. The spectra also show strong droplet size dependence, indicative of the interactions between the molecule and the liquid. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Infrared spectra are reported for [sup 12]C[sub 2]H[sub 2], [sup 13]C[sub 2]H[sub 2], [sup 12]C[sup 13]CH[sub 2], and [sup 12]C[sub 2]HD solvated in superfluid helium nanodroplets, corresponding to excitation of the C–H stretches. For the lowest rotational states (J=0 and J=1), molecular rotation is only weakly hindered by the liquid and the associated transitions are sharp, having small frequency shifts relative to the gas phase. In contrast, the R(1) transitions of [sup 12]C[sub 2]H[sub 2] and [sup 13]C[sub 2]H[sub 2], which access the corresponding J=2 rotational states, are much broader and more strongly shifted from the gas phase. The linewidths of the R(0) transitions show a strong isotopic dependence, which we take as evidence that vibrational resonances present in some of the isotopomers enhance the vibrational relaxation rate. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on the influence of solvents on chemical reaction dynamics. Use of high-resolution spectroscopy to study the vibrational dynamics of molecules in solution; Formation of weakly bound complexes within the superfluid helium droplets.

Psychosocial and psychiatric problems are common in patients admitted to general hospitals, and can negatively influence course of somatic diseases. Hence, early identification and adequate management is important. The aim of this study is to investigate attitudes towards psychosocial and psychiatric problems by non-psychiatrist consultants in an academic hospital. Data were collected by anonymous, self- administered questionnaires which were provided to all consultants during morning reports and by email. Of 431 eligible participants, 187(43%) completed the questionnaire: 64% during morning reports, and 36% by email. Almost all consultants report generally positive attitudes towards mental health problems. However, we identified several obstacles towards management. First, there was a discrepancy between positive attitude and the willingness to take on management responsibility. Reported reasons for this discrepancy were time constraints and lack of skills. We also found that consultants feel little responsibility for the management of depression and chronic drinking. Physicians have generally more positive attitudes than surgeons. Finally, all consultants are less likely to refer patients with dementia and treatment non-compliance to psychiatry, for reasons of perceived ineffectiveness and fear of stigmatizing patients. We conclude targeted education on the management of these problems for hospital consultants is still warranted. [ABSTRACT FROM AUTHOR]

High resolution optothermal spectra have been obtained for the Ar–HCl and Ar–DF complexes which conclusively show that they do not dissociate on H/D–X vibrational excitation. The observed linewidths place a lower limit on the lifetimes of 500 ns, while time-of-flight considerations indicate that the lifetimes are in excess of 0.4 ms. Stark spectra are also reported, which result in the determination of the (v=1) excited state dipole moments of these complexes. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]