Laser induced acoustic desorption (LIAD) has been used for the first time to study the parent ion production and fragmentation mechanisms of a biological molecule in an intense femtosecond (fs) laser field. The photoacoustic shock wave generated in the analyte substrate (thin Ta foil) has been simulated using the hydrodynamic HYADES code, and the full LIAD process has been experimentally characterised as a function of the desorption UV-laser pulse parameters. Observed neutral plumes of densities >10(9) cm(-3) which are free from solvent or matrix contamination demonstrate the suitability and potential of the source for studying ultrafast dynamics in the gas phase using fs laser pulses. Results obtained with phenylalanine show that through manipulation of fundamental femtosecond laser parameters (such as pulse length, intensity and wavelength), energy deposition within the molecule can be controlled to allow enhancement of parent ion production or generation of characteristic fragmentation patterns. In particular by reducing the pulse length to a timescale equivalent to the fastest vibrational periods in the molecule, we demonstrate how fragmentation of the molecule can be minimised whilst maintaining a high ionisation efficiency.

Velocity map imaging methods, with a new and improved ion optics design, have been used to explore the near ultraviolet photodissociation dynamics of gas phase 2-bromo- and 2-iodothiophene molecules. In both cases, the ground (X) and spin-orbit excited (X*) (where X = Br, I) atom products formed at the longest excitation wavelengths are found to recoil with fast, anisotropic velocity distributions, consistent with prompt C–X bond fission following excitation via a transition whose dipole moment is aligned parallel to the breaking bond. Upon tuning to shorter wavelengths, this fast component fades and is progressively replaced by a slower, isotropic recoil distribution. Complementary electronic structure calculations provide a plausible explanation for this switch in fragmentation behaviour—namely, the opening of a rival C–S bond extension pathway to a region of conical intersection with the ground state potential energy surface. The resulting ground state molecules are formed with more than sufficient internal energy to sample the configuration space associated with several parent isomers and to dissociate to yield X atom products in tandem with both cyclic and ring-opened partner fragments.

The inclination of the two aryl rings (ring twists) in a series of benzophenone molecules has been examined. For each structure the dihedral angle (between the planes of the two sets of six aromatic C atoms) relates to both the steric considerations of the single molecule and the packing forces related to the crystal structure. Six new benzophenone structures are incorporated into the study including 2,2'-dihydroxy-4,4'-dimethoxybenzophenone (I), C(15)H(14)O(5), that appears to have the smallest reported twist angle, 37.85 (5) degrees , of any substituted benzophenone reported to date. Three further benzophenones, 4,4'-bis(diethylamino)benzophenone (II), C(21)H(28)N(2)O, 3,4-dihydroxybenzophenone (III), C(13)H(10)O(3), and 3-hydroxybenzophenone (IV), C(13)H(10)O(2), have similar ring twists [49.83 (5), 49.84 (5) and 51.61 (5) degrees , respectively] that are comparable with the value of 54 degrees found for the orthorhombic form of unsubstituted benzophenone. 4-Chloro-4'-hydroxybenzophenone (V), C(13)H(9)ClO(2), has a ring twist of 64.66 (8) degrees that is close to the value of 65 degrees found in the metastable monoclinic form of unsubstituted benzophenone and 2-amino-2',5-dichlorobenzophenone (VI), C(13)H(9)Cl(2)NO(2), has a large ring twist of 83.72 (6) degrees . Comparisons with a further 98 substituted benzophenone molecules from the Cambridge Structural Database (CSD) have been made.

H+3 is the simplest triatomic molecule and plays an important role in laboratory and astrophysical plasmas. It is very stable both in terms of its electronic and nuclear degrees of freedom but is difficult to study in depth in the laboratory due to its ionic nature. In this communication, experimental results are presented for the strong field dissociation of the isotopic analogue D+3, using 30 fs, 800 nm laser pulses with intensities up to 1016 W cm−2. By employing a novel experimental set-up, ions were confined in an electrostatic ion trap so that dissociation of the molecule could be studied as it radiatively cools. It was determined that dissociation could only be observed for molecules in ro-vibrational states relatively close to the dissociation limit, while more tightly bound states demonstrated remarkable stability in even the strongest fields.

An electrostatic trapping scheme for use in the study of light-induced dissociation of molecular ions is outlined. We present a detailed description of the electrostatic reflection storage device and specifically demonstrate its use in the preparation of a vibrationally cold ensemble of deuterium hydride (HD + ) ions. By interacting an intense femtosecond laser with this target and detecting neutral fragmentation products, we are able to elucidate previously inaccessible dissociation dynamics for fundamental diatomics in intense laser fields. In this context, we present new results of intense field dissociation of HD + which are interpreted in terms of recent theoretical calculations.