Experimental and theoretical investigations of ionization/dissociation of cyclopentanone molecule in a femtosecond laser field

Abstract

The ionization/dissociation mechanism of cyclopentanone has been experimentally investigated in molecular beam by irradiating with intense 394 and 788 nm laser fields with pulse duration of 90 fs. The range of laser intensities varied from 3 x 10(13) to 4 x 10(14) W/cm(2). For both wavelengths, the singly charged parent ion is observable while the doubly charged one cannot be found easily, although the fragmentation pattern supports its presence. Meanwhile, the extent of fragmentation at 788 nm is less than that in the 394 nm case. We quantitatively analyze the ionization processes of cyclopentanone in intense femtosecond laser by comparing the calculation results of ionization rate constants obtained from Ammosov-Delone-Krainov, Keldysh, and Keldysh-Faisal-Reiss (KFR) theories based on hydrogenlike atom model. We also compare the experimental and theoretical results; the generalized KFR theory is found to be useful in predicting the ionization yields of singly and doubly charged cyclopentanone ion. To interpret the dissociation patterns of the cyclopentanone ions, we have used the Rice-Ramsperger-Kassel-Marcus theory with the potential surfaces obtained from the ab initio quantum chemical calculations.

Dissociative Ionization and Thermal Decomposition of Cyclopentanone

“…The potential energy surface of the dissociative ionization of C 5 H 8 O presented here differs slightly from that reported previously . First, the lowest energy pathway leading to the C 3 H 4 O+C 2 H 4 reported by Wang et al yields cyclopropanone at an energy of 170.7 kJ mol −1 (1.77 eV) relative to the cation. In this work, we find that this channel is significantly higher (by 0.2 eV) in energy at 1.97 eV with respect to the cation (11.26 eV w.r.t.…”

“…Lastly, a noticeable difference lies in the CO‐loss channel. In addition to the concerted ring opening and hydrogen shift at a barrier of 11.17 eV reported here and by Wang et al., we also located a practically isoenergetic transition state (at 11.18 eV) that involves ring opening followed by migration of a hydrogen (i.e., a non‐concerted channel), making it somewhat more likely to dominate the CO‐loss mechanism. The detection of a very weak signal at m / z 83 indicates that keto–enol tautomerization only plays a minor role in dissociative photoionization.…”

“…Wang et al . performed a combined theoretical and experimental study on the dissociative photoionization of cyclopentanone, providing a detailed C 5 H 8 O .…”

A simple ‘statistical’ approach for fragmentation studies of doubly ionized cytosine, thymine and uracil bases

“…Experiments performed at different collision energy (in the range 25-100 keV) support this assumptions as they revealed similar fragmentation mass spectra, independently of the incident protons energy. Therefore, specific dissociation schemes and associated reaction rates, that are often considered in lower energy processes such as photodissociation [21], are not taken into account here. In this approximation, every atom from the parent molecule can be combined to form all possible correlated A + /B + fragment pairs without any initial geometrical or charge density consideration.…”

Keto-enol tautomerization and intermolecular proton transfer in photoionized cyclopentanone dimer in the gas phase

“…Zewail and co-workers 52 studied the femtosecond photoionization dynamics of CP, and suggested that the fragment ion of m/z 55 originates, out of two distinct possibilities, primarily due to loss of C 2 H 5 • and partly due to the loss of HCO • from the molecular ion. The mass spectra of CP upon ionization by femtosecond laser pulses of several wavelengths were also studied by Wang et al 53 The authors observed that the measured ionization rates display good agreement with the predictions of Keldysh-Faisal-Reiss (KFR) mechanism.…”