Sequential and direct ionic excitation in the strong-field ionization of 1-butene molecules

We study the Strong-Field Ionization (SFI) of the hydrocarbon 1-butene as a function of wavelength using photoion-photoelectron covariance and coincidence spectroscopy. We observe a striking transition in the fragment-associated photoelectron spectra: from a single Above Threshold Ionization (ATI) progression for photon energies less than the cation D0–D1 gap to two ATI progressions for a photon energy greater than this gap. For the first case, electronically excited cations are created by SFI populating the ground cationic state D0, followed by sequential post-ionization excitation. For the second case, direct sub-cycle SFI to the D1 excited cation state contributes significantly. Our experiments access ionization dynamics in a regime where strong-field and resonance-enhanced processes can interplay

Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy

Time-resolved photoelectron spectroscopy was used to obtain new information about the dynamics of electronic relaxation in gas-phase indole and 5-hydroxyindole following UV excitation with femtosecond laser pulses centred at 249 nm and 273 nm. Our analysis of the data was supported by ab initio calculations at the coupled cluster and complete-active-space self-consistent-field levels. The optically bright 1La and 1Lb electronic states of 1\u3c0\u3c0* character and spectroscopically dark and dissociative 1\u3c0\u3c3* states were all found to play a role in the overall relaxation process. In both molecules we conclude that the initially excited 1La state decays non-adiabatically on a sub 100 fs timescale via two competing pathways, populating either the subsequently long-lived 1Lb state or the 1\u3c0\u3c3* state localised along the N-H coordinate, which exhibits a lifetime on the order of 1 ps. In the case of 5-hydroxyindole, we conclude that the 1\u3c0\u3c3* state localised along the O-H coordinate plays little or no role in the relaxation dynamics at the two excitation wavelengths studied.Peer reviewed: YesNRC publication: Ye

Emotion and innner state adverbials in Russian

We study a group of adverbials that are composed of a preposition and a noun denoting an emotion or an inner state. Being collocations, they occupy an intermediate position between free phrases and idioms. On the one hand, some of them are simple adverbial derivatives of nouns and therefore inherit some of their properties. On the other hand, they may have specific properties of their own. Two types of properties of the adverbials are studied: the actantial properties in their correlation with the properties of the source nouns, and the semantics proper

Excited state wavepacket dynamics in NO 2 probed by strong-field ionization

We present an experimental femtosecond time-resolved study of the 399 nm excited state dynamics of nitrogen dioxide using channel-resolved above threshold ionization (CRATI) as the probe process. This method relies on photoelectron-photoion coincidence and covariance to correlate the strongfield photoelectron spectrum with ionic fragments, which label the channel. In all ionization channels observed, we report apparent oscillations in the ion and photoelectron yields as a function of pumpprobe delay. Further, we observe the presence of a persistent, time-invariant above threshold ionization comb in the photoelectron spectra associated with most ionization channels at long time delays. These observations are interpreted in terms of single-pump-photon excitation to the first excited electronic X˜ 2A1 state and multi-pump-photon excitations to higher-lying states. The short time delay (<100 fs) dynamics in the fragment channels show multi-photon pump signatures of higherlying neutral state dynamics, in data sets recorded with higher pump intensities. As expected for pumping NO2 at 399 nm, non-adiabatic coupling was seen to rapidly re-populate the ground state following excitation to the first excited electronic state, within 200 fs. Subsequent intramolecular vibrational energy redistribution results in the spreading of the ground state vibrational wavepacket into the asymmetric stretch coordinate, allowing the wavepacket to explore nuclear geometries in the asymptotic region of the ground state potential energy surface. Signatures of the vibrationally “hot” ground state wavepacket were observed in the CRATI spectra at longer time delays. This study highlights the complex and sometimes competing phenomena that can arise in strong-field ionization probing of excited state molecular dynamics

High Harmonic Spectroscopy of the Cooper Minimum in Molecules

The Cooper minimum (CM) has been studied using high harmonic generation solely in atoms. Here, we present detailed experimental and theoretical studies on the CM in molecules probed by high harmonic generation using a range of near-infrared light pulses from λ = 1.3 to 1.8 µm. We demonstrate the CM to occur in CS₂ and CCl₄ at ~42 and ~40 eV, respectively, by comparing the high harmonic spectra with the known partial photoionization cross sections of different molecular orbitals, confirmed by theoretical calculations of harmonic spectra. We use CM to probe electron localization in Cl-containing molecules (CCl₄, CH₂Cl₂, and trans-C₂H₂Cl₂) and show that the position of the minimum is influenced by the molecular environment

Femtosecond Laser Mass Spectrometry and High Harmonic Spectroscopy of Xylene Isomers

Structural isomers, molecules having the same chemical formula but with atoms bonded in different order, are hard to identify using conventional spectroscopy and mass spectrometry. They exhibit virtually indistinguishable mass spectra when ionized by electrons. Laser mass spectrometry based on photoionization of the isomers has emerged as a promising alternative but requires shaped ultrafast laser pulses. Here we use transform limited femtosecond pulses to distinguish the isomers using two methods. First, we probe doubly charged parent ions with circularly polarized light. We show that the yield of doubly charged ortho-xylene decreases while para-xylene increases over a range of laser intensities when the laser polarization is changed from linear to circular. Second, we probe high harmonic generation from randomly oriented isomer molecules subjected to an intense laser field. We show that the yield of high-order harmonics varies with the positioning of the methyl group in xylene isomers (ortho-, para- and meta-) and is due to differences in the strength of tunnel ionization and the overlap between the angular peaks of ionization and photo-recombination

The layerwise topography of calvarial bones

The study involved serial bone sections of 57 (25 male and 32 female) skulls of adults. Every skullcap specimen was sliced in the coronal plane at 7 certain points. Thickness of bone layers was measured on the posterior surfaces of every slice at 5 points: on the median line, the left and right most lateral points, and the points in the middle between the median one and the most lateral ones. Calvarial bone outer table is on average 0.1-0.3 mm thicker in men than in women, and this parameter increases in the posterior skullcap with a peak of 2.7-4.8 mm, regardless of sex. In both sexes, outer table becomes thinner in lateral skullcap areas. Diploe is on average 0.3-0.4 mm thicker in men than in women, irrespective of skullcap area. In the median zones, diploe is much thicker in the occipital region, while laterally this layer is slightly thicker in the frontal region. Calvarial bone inner (vitreous) table is 0.1-0.2 mm thicker in men than in women, without any relation detected between this parameter and skullcap area. The range of inner table thickness variability is rather narrow, 0.8-1.6 mm, and this parameter manifests pronounced discontinuity. In the median zones, inner table is thicker in the frontal and parietal regions. Thickness of every bone layer is important for trepanation and cranioplasty

Time stretched multi hit 3D velocity map imaging of photoelectrons

The 2D photoelectron velocity map imaging VMI technique is commonly employed in gas phase molecular spectroscopy and dynamics investigations due to its ability to efficiently extract photoelectron spectra and angular distributions in a single experiment. However, the standard technique is limited to specific light source polarization geometries. This has led to significant interest in the development of 3D VMI techniques, which are capable of measuring individual electron positions and arrival times, obtaining the full 3D distribution without the need for inversion, forward convolution, or tomographic reconstruction approaches. Here, we present and demonstrate a novel time stretched, 13 lens 3D VMI photoelectron spectrometer, which has sub camera pixel spatial resolution and 210 ps sigma time of flight TOF resolution currently limited by trigger jitter . We employ a kHz CMOS camera to image a standard 40 mm diameter microchannel plate MCP phosphor anode detector providing x and y positions , combined with a digitizer pick off from the MCP anode to obtain the electron TOF. We present a detailed analysis of time space correlation under data acquisition conditions which generate multiple electrons per laser shot, and demonstrate a major advantage of this time stretched 3D VMI approach that the greater spread in electron TOFs permits for an accurate time and position stamping of up to six electrons per laser shot at a 1 kHz repetition rat