1s-1s electron transfer in collisions of fast C and O ions with adenine

Nuclear Inst. and Methods in Physics Research B 462 (2020) 68–74

Contents lists available at ScienceDirect

Nuclear Inst. and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb

1s-1s electron transfer in collisions of fast C and O ions with adenine a

a

a

a

b

Chandan Bagdia , S. Bhattacharjee , M. Roy Chowdhury , A. Mandal , G. Lapicki , ⁎ Lokesh C. Tribedia, a b

T

Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Dr. Homi Bhaha Road, Colaba, Mumbai 400005, India Department of Physics, East Carolina University, Greenville, NC 27858, USA

ARTICLE INFO

ABSTRACT

Keywords: K-ionization K-K electron transfer Ion-impact Adenine Biomolecules Inner-shell Accelerator ECUSAR-model

1s-1s electron transfer and K-shell ionization cross sections of adenine (C5H5N5) molecule have been measured in collisions with C and O ions in the energy range of 2.5–5.3 MeV/u. These cross sections have been measured from the study of KLL Auger electron yields as a function of projectile charge state. The K-ionization cross section data have been compared with the ECUSAR calculations [ECPSSR model with the perturbed stationary state (PSS) effect calculated in a united and separated atom (USA) approximation]. The K-ionization data shows a good agreement with the model whereas the K-K transfer cross section is underestimated by the same model. Energy dependence of the K-K transfer cross section for adenine is found to be flat compared to that for N2 gas molecules. The values of the K-K e− transfer and the K-ionization cross sections are found to be comparable in this energy range.

1. Introduction

sections of various processes like ionization, electron capture, transfer ionization, DEA and molecular fragmentation are important to calculate the total energy loss inside the matter. Inner shell processes are important to produce the high energy electrons. These higher energy electrons can lead to further ionization and production of low energy electrons causing further damage. We present a study of the state selective 1s-1s (K-K) electron transfer cross sections and the 1s-ionization (KI) cross sections involving adenine molecule, which is a DNA base molecule. Such electron transfer and ionization involving K-shell of atoms in a DNA base molecules have not been studied before. The technique involves the measurement of the double differential cross sections (DDCS) of electron emission spectrum using the ejected electron spectroscopy. The low energy part of the continuum DDCS spectrum reveals various mechanisms of electron emission, such as, soft collision (SC), two center electron emission (TCEE) and binary encounter (BE) etc. [26]. Study of the KLL Auger electron line spectrum is of the particular interest in this work. The state selective K-K electron transfer and KI cross sections have been measured using projectile charge state (qp ) dependence of the KLL Auger electron yield. The measurement of the K-K transfer cross sections using the qp dependence of K X-ray yield is well established technique [27–34]. But as far as the K-K transfer using Auger technique is concerned there are only fewer studies. However, these studies [35–37] addressed different aspects using different techniques, such as, impact parameter

Study of electron emission upon ion impact has now been pursued for several decades to understand various fundamental processes and collision dynamics in atoms and molecules. Experimental as well as theoretical studies involving biologically relevant molecules, such as, the base molecules of DNA/RNA and water etc., received a special attention by the scientific community [1–22]. These studies have a wide range of application in the radiation physics, medical science and radiology etc. The energy loss curve of high energy ions in interaction with matter has a special feature. The ions deposit most of its energy at the end of its track, i.e. in the Bragg peak region. Due to this feature, high energy ion beams from an accelerator are proved to be very efficient to remove cancer or tumor in human body. In hadron therapy, the high energy (proton or carbon) ion beams are made to pass through the living cells which results in the damage of the cells. It has been established that the secondary electrons emitted upon ion impact contribute to the single and double strand breakage of DNA/RNA molecules via dissociative electron attachment (DEA) [1]. The secondary electrons of higher energy also induce such double-strand breaks in DNA/RNA due to other processes, such as, ionization and fragmentation etc. [2]. To understand the various mechanisms of the cellular damage, different groups have reported studies on electron emission and molecular fragmentation upon ion impact [4–13,15,17,23–25], and ionization upon electron impact [1,2,18–22] etc. Measurements of the cross

⁎

Corresponding author. E-mail address: [email protected] (L.C. Tribedi).

https://doi.org/10.1016/j.nimb.2019.11.004 Received 27 August 2019; Received in revised form 27 October 2019; Accepted 4 November 2019 0168-583X/ © 2019 Elsevier B.V. All rights reserved.

Nuclear Inst. and Methods in Physics Research B 462 (2020) 68–74

C. Bagdia, et al.

dependence [35] and coincidence measurement of Auger electron and recoil charge state [36,37]. Auger electron in coincidence with post collisional projectile charge state is used to investigate the transfer cross sections [38,39] which was limited to proton only. The qp dependence of the projectile Auger electron emission is also used to study the electron transfer process [40–42], in general. For the atoms with low atomic number (Z), such as, C and N, the Kshell fluorescence yields are typically less than 1% [43], for which the K-vacancies preferably get filled via Auger process. Therefore the Auger electron detection is an efficient way to study the inner shell vacancy for these low Z atoms as compared to the X-ray measurements. Also, it is difficult to measure the K-K electron transfer cross section in the case of a symmetric or near symmetric collision system (i.e. if projectile Z target Z) since X-rays from such projectile and target are not easily separable. The study of symmetric and near symmetric collision system is important as it involves resonant or near resonant electron transfer from target to projectile. Here the resonant system is represented by the collision partners having same K-shell binding energies. Similarly near symmetric system implies K-binding energies which are close. The present experiment is aimed to measure K-shell processes for adenine molecule which involves the near symmetric collisions. There exists only one measurement by Woods et al. [44,45] which provided the table of KLL Auger-cross section for N, O, F and Cl ions colliding on Ne. Its possible to derive the K-K transfer cross sections from these data. It has indicated a substantial enhancement in the target KLL-Auger cross section for the projectiles with K-vacancy because of the K-K transfer. In this study, we have measured the state selective K-K transfer and the KI cross sections from constituent atoms of the adenine molecule (C5H5N5) upon the impact of C and O ions. The total contribution from the entire molecule has also been deduced. The energy dependence of these cross sections are also studied i.e. in the energy range 2.5 to 5.25 MeV/u. These cross sections for N2 gas have also been measured and the data have been compared with that for the N atom in the adenine. The measured data have been compared with the ECUSAR calculations. The model ECUSAR is a modification of the ECPSSR model [46,47]. In the ECUSAR, the perturbed stationary state (PSS) approximation has been used in a united and separated atom (USA) approach along with the energy loss (E), the Coulomb deflection (C), and the relativistic (R) corrections [48]. In Section 2, the experimental setup including the target preparation has been briefly described. In Section 3, the absolute normalization procedure, the measurement technique and the data analysis procedure have been discussed. In Section 4, the results on the energy dependence of the KI and transfer cross sections, the projectile Z dependence and comparisons between the transfer and ionization cross sections are presented.

Fig. 1. A schematic diagram of the heater assembly with a thickness monitor mounted from the XYZ manipulator.

heater current anyway. The spectrometer was used to measure the secondary electrons with energy between 1 and 600 eV. The CEM has highest and flat efficiency curve for electrons in the energy range of 100–600 eV [51]. To improve the detection efficiency of the low energy electrons the CEM front was raised to a positive 100 V. A LabVIEW based data acquisition system was used to scan the voltages on the hemispheres of the spectrometer and record the spectra. 2.2. Target preparation An effusive vapor jet was prepared by heating the adenine powder ( 99% purity) in an oven assembly (Fig. 1). The powder was filled in a copper molecular holder with a nozzle of aspect ratio 10 (length 15 mm, diameter 1.5 mm). A thermocouple was used to monitor the temperature of the oven. Maintaining a uniform vapor density throughout the experiment is very crucial. To achieve this, a slow uniform heating is extremely important which was achieved by using a fine control ( 10 mV) on the voltage applied on the heating coil of the oven. The thermocouple signal was amplified using an amplifier to read the output voltage with a better precision. The adenine powder was kept around 100 °C for 2–3 h to remove all the moisture absorbed in the molecules. And then it was slowly heated to approximately 148 °C in the time period of about 24 h to reach appropriate and steady target density. To avoid the possible dark counts at the CEM, the heater was covered with a water cooled jacket. The quartz-crystal based thickness monitor was mounted above the vapor jet [52]. By monitoring the deposition rate of the adenine molecules during measurements, the uniformity of the flow rate is ensured. Fig. 2 shows the deposition rate as a function of time for over 50 h. The maximum variation in the deposition rate has been found to be 10%. The measurements with gaseous target, N2, was performed by flooding the interaction chamber with the target gas at low pressure. The absolute target gas pressure inside the interaction chamber was measured by a capacitance manometer (MKS Baratron). The static gas pressure control was achieved using a solenoid valve with the MKS Baratron readings as feedback. The typical gas pressure has been maintained at 0.15–0.20 mTorr for the measurements.

2. Experimental details 2.1. Experimental setup Experiments were performed using C and O ion beams of energies between 2.5 and 5.3 MeV/u. The well collimated parallel ion beams of different charge states were obtained from the Pelletron accelerator at TIFR, Mumbai [49]. The high vacuum scattering chamber was maintained to base pressure of 6 × 10 8 mbar. An electrostatic hemispherical spectrometer was used to analyze the energy of the ejected electrons [50]. A channel electron multiplier (CEM) was used to detect these electrons. Two µ -metal sheets were placed inside the chamber to reduce the Earth’s magnetic field to 10 mG level. The change in magnetic field due to the current used to heat the adenine target was found to be negligible. It was also confirmed by looking into the shape of the low energy electron spectrum which was unaffected in presence of the heating current. However, it may be mentioned that the present experiment is concerned with the higher energy (KLL Auger) electrons for which there is no influence for the 69

Nuclear Inst. and Methods in Physics Research B 462 (2020) 68–74

C. Bagdia, et al.

the gas present and for background run respectively. The quantity = 0.06(Vc + e ) is the spectrometer resolution, where, Vc is the preacceleration potential and e is the electron energy. The quantity el is the detection efficiency of the CEM and the (l )eff represents the solid angle path length integral. The number density of target is denoted by n. In case of the experiment with the flooded chamber, the static gas density has been determined from the absolute gas pressure. The gas density is constant throughout the path length, thus the (l )eff has been obtained from the spectrometer geometry, by integrating solid angle over the path length. In order to obtain the abs ,the (l )eff was multiplied by n [50,53]. In the case of the adenine jet, the vapor density across the path length of the spectrometer is not constant and hence the density profile [ J (Z )] has been calculated using the Scoles’ formalism [54]. For the absolute number density, not only the target density profile, but also the vapor pressure of adenine is required. The vapor pressure is a strong function of the temperature, which may not be known precisely. Also the temperature measurement inside the molecule holder is not that accurate. Hence for the absolute normalization, the following procedure has been adopted which is based on the KLL-Auger yields of N. An assumption has been made that the total Auger electron emission cross sections per N atom in N2 gas and in adenine vapor are the same since it is an inner shell process. The absolute DDCS of e− emission from the N2 target was obtained from the first principle, using Eq. (1). The DDCS has been integrated over all the angles to get the single differential cross section (SDCS). The absolute total Auger cross section for N [ abs (N KLL , N2) ] was obtained by integrating the SDCS spectrum over the N-KLL Auger peak energy range as given by Eq. (2), i.e.,

Fig. 2. Measured deposition rate of adenine molecules with time. The solid line represents a linear fit of the measured values and the dashed line indicate a variation of 10%.

3. Data analysis The typical DDCS spectra of the electron emission from adenine molecule is shown in Fig. 3. The peaks at 240 eV and 355 eV in the spectrum correspond to the carbon and nitrogen KLL Auger electron, respectively. The KLL Auger peak ride on the continuum electron emission spectrum arising from the Coulomb ionization of outer shells. By measuring the area under the Auger peak and integrating over the angles we obtain the total KLL-Auger electron emission cross section ( KLL ). The detailed analysis and the normalization process to obtain the absolute DDCS spectrum has been described in the following section.

abs (N

3.1. Absolute normalization

d 2 abs = d ed e

(

el

Nb ( e , e ) N p

n (l )eff

d

Auger

).

ed

d

ed

e

e.

(2)

The relative DDCS ( rel ) for adenine has been obtained using the convoluted jet profile density and the solid angle integrated over path length, according to Eq. (3), i.e.,

To obtain the DDCS spectrum as shown in Fig. 3, at a given angle, the energy spectrum has been taken with and without target gas. A sufficiently long Faraday cup is used to prevent the backscattered electrons from beam dump to re-enter the chamber. The absolute cross section ( abs ) has been calculated by the first principle as described by relation given by, Ne ( e , e ) Np

abs N2

d2

KLL , N2) =

d 2 rel = d ed e

( el

Ne ( e , e ) Np

Nb ( e , e ) N p

)

(l ( ( , Z ) × J (Z )))eff

.

(3)

The relative DDCS for adenine has been integrated over all the angles to obtain the SDCS. Further integration over the KLL peak in the SDCS spectrum provides the relative KLL-Auger e− cross section [ rel (N KLL , Adenine )] for N in adenine (see Eq. (4)).

(1)

The Ne , Nb are the number of electrons detected with and without gas respectively. The Np, N p are the number of projectile ions in case of

rel (N

KLL , Adenine ) = Auger

d2 d

rel Adenine ed

e

d

ed

e

(4)

The normalization constant (K) has been obtained using Eq. (5), i.e.,

K=

abs (N rel (N

KLL, N2)/2 . KLL , Adenine )/5

(5)

The numerator and denominator was divided by 2 and 5 respectively to take care of the number of N atoms in N2 and adenine (C5H5N5). This normalization constant has been used to obtain absolute DDCS for adenine as given by Eq. 6,

d2 d

abs Adenine ed

e

=K×

d2 d

rel Adenine ed

e

.

(6)

The value of K was found to be 2.19 × 10 18 and the value calculated by using the vapor pressure [55] of adenine at 148 °C is 1.36 × 10 18. The difference in the K value arises due to the fact that the temperature is measured at the body of the oven, but not directly in the powder. Observed difference corresponds to the powder temperature of 146 °C.

Fig. 3. Typical DDCS spectrum of electrons emitted from adenine under the bombardment of 60 MeV C6 + ions. 70

Nuclear Inst. and Methods in Physics Research B 462 (2020) 68–74

C. Bagdia, et al.

3.2. Derivation of K-K electron transfer cross section For projectile with no K-shell vacancy, the target KLL-Auger electron emission will be due to K-ionization. The projectile with the Kvacancy will result in the K-shell vacancy production in the target because of the K-ionization as well as the K-K electron capture. Hence by measuring the qp dependence of the KLL-Auger electron cross section, i the electron transfer cross section can be calculated. The KLL represents the KLL-Auger cross section for ’i’ (0,1,2) vacancy in the projectile. The 0 KLL corresponds to K-shell ionization cross sections. Hence to calculate the K-K electron transfer cross section K K , Eq. (7) or Eq. (8) has been used: K K

=

1 KLL

K K

=

1 ×( 2

(7)

0 KLL,

2 KLL

0 KLL ).

(8)

The electron transfer from target K-shell to the projectile L-shell, in principle, can produce KLL-Auger electron. We have estimated the K-L transfer contribution using the ECUSAR model and found that the contribution is very small. This was also supported by earlier experimental data [44] on the KLL Auger process, for collision systems which are similar to the present systems (see inset in Fig. 4). The plot shows that the KLL-Auger cross section is not varying significantly as a function of the projectile L-vacancy. If there was significant K-L transfer then the target KLL Auger yield would have increased with the increasing L-vacancy. Hence, the contribution of the K-L transfer is negligible in this energy range for near symmetric collision systems. A typical spectrum of Auger electron cross section vs qp has been shown in Fig. 4. The projectiles with the K-shell vacancy (C5+ and C6 +) show enhancement in the Auger electron emission cross section as compared to the projectiles with no K-shell vacancy (C4 + ). Hence by using Eq. (7) and (8) the K K has been determined. The overall uncertainty in the absolute K-ionization cross section measurements was estimated to be about 20–22% which mainly arises from the adenine vapor density fluctuation (10%), the normalization procedure (18%), the statistical uncertainty (about 3–5%), solid-angle path length (8%) etc. For the K-K transfer cross sections, additional error arises due to the subtraction of KI which results in overall uncertainty of about 25–30%.

Fig. 5. Energy dependence of the KI for different target projectile combination as denoted in each panel. The solid and dashed lines represent the ECUSAR and the first Born calculations, respectively.

comparison between the KI and K-K transfer cross sections. The Auger electron production cross sections have been measured at 150° angle for the various charge states. For carbon ion, the chosen energies are 30, 42, 51 and 60 MeV. In the case of oxygen ions, we have used following energies: 40, 56, 68 and 85 MeV. The obtained Auger cross sections have been multiplied by 4 considering an isotropic distribution of these electrons to obtain total cross section. 4.1. Energy dependence of KI cross sections The K-shell ionization cross sections are shown in Fig. 4. The energy dependence of the KI for C and N atoms from the adenine molecule in collisions with C ions and that from the N2 have been plotted in Fig. 5 (a, b). For the C ions, the KI of C atom in adenine tends to decrease with the energy. These are very well reproduced by the ECUSAR and the B1 (first Born) calculations. The derived KI values for the C ions on N atom in adenine and that for the N2 molecules are found to be the same and well reproduced by the ECUSAR calculations [Fig. 5(b)]. For the O ions on the C and N atoms in adenine, the KI shows decreasing trend and are in very good agreement with the ECUSAR calculations as shown in Fig. 5(c, d). The total KI cross section for the adenine molecule has been calculated by adding individual atomic contributions. The H atom contribution would be negligibly small as it does not contribute to the strongly bound inner shell ionization. The energy dependence of the total KI cross sections has been plotted in Fig. 6 along with the ECUSAR and the B1 calculations. The ECUSAR calculations show good agreement with the data.

4. Results and discussions In this section, the measured K-ionization and K-K electron transfer cross sections for adenine and N2, the projectile energy and Z-dependence of these cross sections have been discussed along with the

4.2. Energy dependence of K-K transfer cross sections The K-K e− transfer cross sections have been determined using the Eq. (7) and Eq. (8). Fig. 7 shows the energy dependence of the K K for the C and N atoms in adenine molecule. Energy dependence of the data for N atom in N2 molecule has also been plotted in Fig. 7. All the cross sections plotted in Fig. 7 are normalized to per atom per K-vacancy. The calculations based on the ECUSAR model (solid line) shows a large deviation. The dashed line represents the same calculations which is normalized at one point with measured data to compare the energy dependence. The K K data in collisions with the C ions with N atom in adenine and N atom in N2 molecule, do not show much difference

Fig. 4. The projectile charge state dependence of the Auger electron production cross section for 51 MeV C-ions on N2. The dashed line represents guide to eye. Inset: KLL from Table III of Woods et al. [44], for O and F ions on Ne. 71

Nuclear Inst. and Methods in Physics Research B 462 (2020) 68–74

C. Bagdia, et al.

Fig. 6. Energy dependence of the total KI for adenine. The square represents measured data, solid and dashed lines represent values obtained from the ECUSAR and the first Born calculations, respectively.

Fig. 8. Energy dependence of the total K K for adenine. Solid lines: ECUSAR model prediction. Dashed lines: same calculations normalized to the measured data at one point.

by adding the contribution of C and N atoms, whereas the negligible contribution from H has been neglected. Energy dependence of the total K K for adenine has been plotted in Fig. 8. The K K has flat energy dependence for both the projectiles. Absolute values show a large deviations from the ECUSAR calculations. Hence the trend of the energy dependence has been compared with the dashed line which is obtained by normalizing the ECUSAR model at one point (Fig. 8). The calculations show a decreasing trend with the energy whereas, the data is flat for both the C and O ions. 4.3. KI vs K-K e− transfer cross sections Fig. 9 shows the energy dependence of the ratio, of the total K K to We have compared the data with the ECUSAR model. The normalized ECUSAR calculation for the K K (i.e. dashed line in Fig. 8) was used to obtain the ratios. The data for C ions show almost a flat behavior with the energy, whereas the calculations show decreasing trend. In case of the O ions, the data shows increasing trend contrary to the calculation which shows decreasing trend. We also find that in this energy range, the K K is comparable to the KI . The ratio of K K to KI varies from 20% to 50%. The inset in each panel of Fig. 9 shows the variation of the absolute value of ratio calculated using ECUSAR model over wider energy range for C and O ion projectiles. The calculated ratios are smaller than the measured data for both the projectiles and deviation from absolute values increases with the energy. Hence, it may be important to include the K-K transfer process along with KI for modeling the energy loss and radiation therapy. KI .

Fig. 7. Energy dependence of the K K for different target projectile combination [as denoted in figure]. Solid lines: the ECUSAR model predictions. Dashed lines: the same calculation normalized to the measured data at one point.

quantitatively. The K K tend to decrease with energy for the target N2 whereas in case of the adenine target, the energy dependence is rather flat. The K K for the O ions on C and N atoms in adenine show almost energy independence in this energy range. The ECUSAR calculations show a large deviation from the data. The deviation with the model prediction increases with the energy. The qualitative trend of the normalized calculations matches with the data for the N2 molecule at higher energies. The data for the adenine show clear deviation even with the trend of the normalized calculations for C and O ions. The total K K data for the adenine molecule has also been deduced

4.4. Projectile Z-dependence of KI and K-K transfer cross sections Fig. 10 shows the projectile Z dependence of the 72

KI

and

K K

for

Nuclear Inst. and Methods in Physics Research B 462 (2020) 68–74

C. Bagdia, et al.

5. Conclusions The measurement of the K-K e-transfer and K-ionization cross sections involving a DNA-base molecule has been reported for the first time. The energy dependence of the K K and KI in the range of 2.5 MeV/u to 5.3 MeV/u have been measured for C and O ion beams. The measured KI show a very good agreement with the ECUSAR calculations whereas the same model underestimates the K K data. For the near symmetric systems the transfer cross section increases rapidly due to the matching of binding energies of initial (target) state and final (projectile) state which gives rise to a substantial overlap of their momentum wave functions. On the other hand, the model used here is mainly of perturbative nature which is normally applied for the asymmetric systems at high velocities. In case of the K-ionization process the binding energy matching condition is not a pre-requisite and therefore the agreement with the model is very good. It may be pointed out that for the K-K transfer in near symmetric systems, non-perturbative theory, such as, close-coupling calculation may be used which is beyond the scope of the present study. The energy dependence of the K K for the constituent N-atom in adenine has been compared with that in N2 gas. It does not show significant difference quantitatively but the energy dependence is flat for the N atom in adenine whereas it shows decreasing trend for the N2 gas molecules. The total KI and K K for adenine has also been deduced by adding contributions of individual constituent atoms. The ratio of the K K to KI has been found to be quite high in this energy range contrary to that predicted in the model. Hence it is important to include the contribution of K-K transfer in modeling the radiological effect. Projectile Z-dependence of the K K for adenine has found to be very weak function of the Z unlike OBKN prediction of Z5 . Finally it may be commented that, it is important to use experimentally measured KI and K K values as an input to calculate the radiation dosage required in hadron therapy.

Fig. 9. Energy dependence of the ratio of K K to KI for adenine. The square represents measured data, the dashed line represents the ratio of normalized ECUSAR ECUSAR to KI . Inset shows the calculated absolute ratio of KECUSAR to K K K ECUSAR over wider energy range. KI

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments We thank the Pelletron accelerator team for smooth running of the machine during the experiment, and W. Fernandes, K. V. Thulasiram, N. Mhatre and S. N. Manjarekar for their assistance during the experiments. References [1] B. Boudaiffa, P. Cloutier, D. Hunting, M.A. Huels, L. Sanche, Resonant formation of dna strand breaks by low-energy (3 to 20 ev) electrons, Science 287 (2000) 1658–1660. [2] B. Boudaiffa, D. Hunting, P. Cloutier, M.A. Huels, L. Sanche, Induction of singleand double-strand breaks in plasmid dna by 100–1500 ev electrons, Int. J. Radiat. Biol. 76 (2000) 1209–1221. [3] D. Schardt, T. Elsässer, D. Schulz-Ertner, Heavy-ion tumor therapy: physical and radiobiological benefits, Rev. Mod. Phys. 82 (2010) 383–425. [4] J. Tabet, S. Eden, S. Feil, H. Abdoul-Carime, B. Farizon, M. Farizon, S. Ouaskit, T.D. Märk, Absolute total and partial cross sections for ionization of nucleobases by proton impact in the bragg peak velocity range, Phys. Rev. A 82 (2010) 022703 . [5] A.N. Agnihotri, S. Nandi, S. Kasthurirangan, A. Kumar, M.E. Galassi, R.D. Rivarola, C. Champion, L.C. Tribedi, Doubly differential distribution of electron emission in ionization of uracil in collisions with 3.5-mev/u bare c ions, Phys. Rev. A 87 (2013) 032716 . [6] A. Itoh, Y. Iriki, M. Imai, C. Champion, R.D. Rivarola, Cross sections for ionization of uracil by mev-energy-proton impact, Phys. Rev. A 88 (2013) 052711 . [7] Y. Iriki, Y. Kikuchi, M. Imai, A. Itoh, Absolute doubly differential cross sections for ionization of adenine by 1.0-mev protons, Phys. Rev. A 84 (2011) 032704 . [8] Y. Iriki, Y. Kikuchi, M. Imai, A. Itoh, Proton-impact ionization cross sections of adenine measured at 0.5 and 2.0 mev by electron spectroscopy, Phys. Rev. A 84 (2011) 052719 . [9] A.N. Agnihotri, S. Kasthurirangan, S. Nandi, A. Kumar, M.E. Galassi, R.D. Rivarola,

Fig. 10. The projectile Z dependence, for adenine and its constituent elements, of the KI (a,b,c) and K K (d,e,f) are plotted. Dashed lines represent the B1 prediction, Z2 dependence for ionization. Dotted lines represent, Z5 dependence based on OBKN approximation [56,57] for transfer cross sections. The data is for ions with the energy 2.5 MeV/u. Both the dashed and dotted lines are normalized at one point i.e. for Z= 6.

adenine and its constituent atoms in panels (a,b,c) and (d,e,f), respectively. The data are plotted for the C and O ions of energy 2.5 MeV/u. According to the B1 prediction KI Z2 (dashed line). The data follows the first Born curve for C and O projectiles. Dotted lines in the Fig. 10 (d,e,f) represent the Z5 dependence as predicted by the OBKN approximation [56,57] for the K-K transfer. It is normalized at the measured K K data for C-ion. Clearly the scaled OBKN prediction overestimates the data. 73

Nuclear Inst. and Methods in Physics Research B 462 (2020) 68–74

C. Bagdia, et al.

[10]

[11] [12]

[13]

[14]

[15] [16]

[17] [18] [19] [20] [21] [22] [23] [24]

[25] [26] [27] [28] [29]

[30] [31] [32]

O. Fojón, C. Champion, J. Hanssen, H. Lekadir, P.F. Weck, L.C. Tribedi, Ionization of uracil in collisions with highly charged carbon and oxygen ions of energy 100 kev to 78 mev, Phys. Rev. A 85 (2012) 032711 . J. Tabet, S. Eden, S. Feil, H. Abdoul-Carime, B. Farizon, M. Farizon, S. Ouaskit, T.D. Märk, 20-150-kev proton-impact-induced ionization of uracil: Fragmentation ratios and branching ratios for electron capture and direct ionization, Phys. Rev. A 81 (2010) 012711 . S. Bhattacharjee, S. Biswas, J.M. Monti, R.D. Rivarola, L.C. Tribedi, Double-differential cross section for ionization of h2 O molecules by 4-mev/u c6 + and si13 + ions, Phys. Rev. A 96 (2017) 052707 . S. Nandi, S. Biswas, A. Khan, J.M. Monti, C.A. Tachino, R.D. Rivarola, D. Misra, L.C. Tribedi, Double-differential cross sections for ionization of h2o by fast bare o ions: Comparison with continuum-distorted-wave eikonal-initial-state calculations in prior and post forms, Phys. Rev. A 87 (2013) 052710 . S. Bhattacharjee, S. Biswas, C. Bagdia, M. Roychowdhury, S. Nandi, D. Misra, J.M. Monti, C.A. Tachino, R.D. Rivarola, C. Champion, L.C. Tribedi, Double differential distribution of electron emission in the ionization of water molecules by fast bare oxygen ions, J. Phys. B: At. Mol. Opt. Phys. 49 (2016) 065202 . C. Champion, M. Galassi, P. Weck, S. Incerti, R. Rivarola, O. Fojón, J. Hanssen, Y. Iriki, A. Itoh, Proton-induced ionization of isolated uracil molecules: A theory/ experiment confrontation, Nucl. Instrum. Methods Phys. Res. Section B 314 (2013) 66–70 Eighth International Symposium on Swift Heavy Ions in Matter (SHIM 2012). S. Sato, Z. He, M. Kaneda, M. Imai, H. Tsuchida, A. Itoh, Electron energy spectra from various amino acids bombarded by 2.0 mev he+ ions, Nucl. Instrum. Methods Phys. Res. Section B 256 (2007) 506–509. Atomic Collisions in Solids.. M. Shimizu, M. Kaneda, T. Hayakawa, H. Tsuchida, A. Itoh, Stopping cross sections of liquid water for mev energy protons, Nucl. Instrum. Methods Phys. Res., Sect. B 267 (2009) 2667–2670 Proceedings of the 23rd International Conference on Atomic Collisions in Solids.. L. Sadr-Arani, P. Mignon, H. Chermette, H. Abdoul-Carime, B. Farizon, M. Farizon, Fragmentation mechanisms of cytosine, adenine and guanine ionized bases, Phys. Chem. Chem. Phys. 17 (2015) 11813–11826. M.A. Rahman, E. Krishnakumar, Communication: Electron ionization of dna bases, J. Chem. Phys. 144 (2016) 161102 . B.F. Minaev, M.I. Shafranyosh, Y.Y. Svida, M.I. Sukhoviya, I.I. Shafranyosh, G.V. Baryshnikov, V.A. Minaeva, Fragmentation of the adenine and guanine molecules induced by electron collisions, J. Chem. Phys. 140 (2014) 175101 . I.I. Shafranyosh, M.I. Sukhoviya, M.I. Shafranyosh, L.L. Shimon, Formation of positive and negative ions of thymine molecules under the action of slow electrons, Tech. Phys. 53 (2008) 1536–1540. I.I. Shafranyosh, M.I. Sukhoviya, M.I. Shafranyosh, Absolute cross sections of positive- and negative-ion production in electron collision with cytosine molecules, J. Phys. B: At. Mol. Opt. Phys. 39 (2006) 4155. M. Rahman, E. Krishnakumar, Absolute partial and total electron ionization cross sections of uracil, Int. J. Mass Spectrom. 392 (2015) 145–153. L.C. Tribedi, A.N. Agnihotri, M.E. Galassi, R.D. Rivarola, C. Champion, Ionization of uracil in collisions with fast bare ions, Eur. Phys. J. D 66 (2012) 303. A.N. Agnihotri, S. Kasthurirangan, S. Nandi, A. Kumar, C. Champion, H. Lekadir, J. Hanssen, P.F. Weck, M.E. Galassi, R.D. Rivarola, O. Fojón, L.C. Tribedi, Absolute total ionization cross sections of uracil (c 4 h 4 n 2 o 2) in collisions with mev energy highly charged carbon, oxygen and fluorine ions, J. Phys. B: At. Mol. Opt. Phys. 46 (2013) 185201 . R. Brédy, J. Bernard, L. Chen, G. Montagne, B. Li, S. Martin, Fragmentation of adenine under energy control, J. Chem. Phys. 130 (2009) 114305 . N. Stolterfoht, R.D. DuBois, R.D. Rivaola, Electron Emission in Heavy Ion Atom Collision, Springer, Berlin, 1997. J. Hall, P. Richard, T.J. Gray, J. Newcomb, P. Pepmiller, C.D. Lin, K. Jones, B. Johnson, D. Gregory, Systematics of single and double k-shell-vacancy production in titanium bombarded by heavy ions, Phys. Rev. A 28 (1983) 99–110. K. Wohrer, A. Chetioui, J.P. Rozet, A. Jolly, C. Stephan, K-k transfer cross sections in near-symmetric fe 26+ ion-atom collisions at intermediate velocity, J. Phys. B: At. Mol. Phys. 17 (1984) 1575. J. Hall, P. Richard, P.L. Pepmiller, D.C. Gregory, P.D. Miller, C.D. Moak, C.M. Jones, G.D. Alton, L.B. Bridwell, C.J. Sofield, Energy systematics of single and double kshell-vacancy production in titanium bombarded by chlorine ions, Phys. Rev. A 33 (1986) 914–920. L.C. Tribedi, K.G. Prasad, P.N. Tandon, K, Phys. Rev. A 47 (1993) 3739–3747. L.C. Tribedi, K.G. Prasad, P.N. Tandon, Z. Chen, C.D. Lin, Single and double k-shell ionization and electron-transfer cross sections for fe and ni bombarded by s ions and fe by si ions at 1.25-4.70 mev/amu, Phys. Rev. A 49 (1994) 1015–1020. B.B. Dhal, L.C. Tribedi, U. Tiwari, P.N. Tandon, T.G. Lee, C.D. Lin, L. Gulyás, Strong

[33]

[34] [35]

[36]

[37]

[38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50]

[51] [52] [53] [54] [55] [56] [57]

74

double k-k transfer channel in near symmetric collision of si+ar at intermediate velocity range, J. Phys. B: At. Mol. Opt. Phys. 33 (2000) 1069. B.B. Dhal, L.C. Tribedi, U. Tiwari, K.V. Thulasiram, P.N. Tandon, T.G. Lee, C.D. Lin, L. Gulyás, State-selective k-k electron transfer and k ionization cross sections for ar and kr in collisions with highly charged c, o, f, s, and cl ions at intermediate velocities, Phys. Rev. A 62 (2000) 022714 . A.K. Saha, L.C. Tribedi, B.B. Dhal, U. Tiwari, P.N. Tandon, Subshell resolved l-k electron transfer and ionization of yb with si ion impact, Phys. Scr. 1999 (1999) 391. S. Hagmann, C.L. Cocke, J.R. Macdonald, P. Richard, H. Schmidt-Böcking, R. Schuch, Quasiresonant charge transfer in inner-shell excitation: Impact-parameter dependence of k-vacancy creation in f q + Ne collisions, Phys. Rev. A 25 (1982) 1918–1929. S. Hagmann, S. Kelbch, C.L. Cocke, P. Richard, A. Skutlartz, H. Schmidt-Böcking, R. Schuch, B. Johnson, M. Meron, K. Jones, Recoil-charge-state–target-k-augerelectron coincidences: a technique to study excitation patterns in k-k charge transfer, Phys. Rev. A 34 (1986) 2897–2910. S. Hagmann, S. Kelbch, H. Schmidt-Böcking, C.L. Cocke, P. Richard, R. Schuch, A. Skutlartz, J. Ullrich, B. Johnson, M. Meron, K. Jones, D. Trautmann, F. Rösel, K-k charge transfer and electron emission for 0.13-mev/u f 8 + +ne collisions, Phys. Rev. A 36 (1987) 2603–2612. C.L. Cocke, R.K. Gardner, B. Curnutte, T. Bratton, T.K. Saylor, k-shell capture by protons from o2, n2, and ne, Phys. Rev. A 16 (1977) 2248–2255. F. McDaniel, A. Toten, R. Bhalla, G. Lapicki, Carbon k-shell vacancy production and k-k electron capture cross sections for 0.4–1.5 mev 11h+ ions incident on ch4 targets, Nucl. Instrum. Methods Phys. Res., Sect. A 240 (1985) 492–497. J. Newcomb, T.R. Dillingham, J. Hall, S.L. Varghese, P.L. Pepmiller, P. Richard, Electron capture by metastable projectiles on he and ne, Phys. Rev. A 29 (1984) 82–91. J. Newcomb, T.R. Dillingham, J. Hall, S.L. Varghese, P.L. Pepmiller, P. Richard, Charge-state dependence of fluorine-projectile k auger-electron production, Phys. Rev. A 30 (1984) 106–111. T.R. Dillingham, J. Newcomb, J. Hall, P.L. Pepmiller, P. Richard, Projectile k-augerelectron production by bare, one-, and two-electron ions, Phys. Rev. A 29 (1984) 3029–3038. M.O. Krause, Atomic radiative and radiationless yields for k and l shells, J. Phys. Chem. Ref. Data 8 (1979) 307–327. C.W. Woods, R.L. Kauffman, K.A. Jamison, N. Stolterfoht, P. Richard, k-shell augerelectron production cross sections from ion bombardment, Phys. Rev. A 13 (1976) 1358–1369. C.W. Woods, R.L. Kauffman, K.A. Jamison, N. Stolterfoht, P. Richard, k-shell augerelectron hypersatellites of ne, Phys. Rev. A 12 (1975) 1393–1398. W. Brandt, G. Lapicki, Energy-loss effect in inner-shell coulomb ionization by heavy charged particles, Phys. Rev. A 23 (1981) 1717–1729. G. Lapicki, F.D. McDaniel, Electron capture from k shells by fully stripped ions, Phys. Rev. A 22 (1980) 1896–1905. G. Lapicki, The status of theoretical l-subshell ionization cross sections for protons, Nucl. Instrum. Methods Phys. Res., Sect. B 189 (2002) 8–20. S.D. Narvekar, R.R. Hosangadi, L.C. Tribedi, R.G. Pillay, K.G. Prasad, P.N. Tandon, A simple post-accelerator foil stripper assembly for atomic collision experiments, Pramana 39 (1992) 79–84. D. Misra, K. Thulasiram, W. Fernandes, A.H. Kelkar, U. Kadhane, A. Kumar, Y. Singh, L. Gulyás, L.C. Tribedi, Double differential distributions of electron emission in ion-atom and electron-atom collisions using an electron spectrometer, Nucl. Instrum. Methods Phys. Res., Sect. B 267 (2009) 157–162. Dr. Sjuts Optotechnik GmbH, n.d. http://www.sjuts.com/Quality_efficiencies.html, accessed: 2017-11-16. INFICON, n.d. http://products.inficon.com/en-us/product/detail/sqm-160, accessed: 2017-11-16. G.W. Kerby, Absolute doubly differential cross sections for ejection of electrons in three- and five-body collisions of 20 to 114 keV protons on atomic and molecular hydrogen, PhD dissertation, University of Nebraska-Lincoln, 1994. Unpublished. G. Scoles, Atomic and Molecular Beam Methods vol. 1, Oxford University Press, New York, 1988, pp. 83–90. W. Zielenkiewicz, Enthalpies of sublimation and vapor pressures of adenine, 1methyladenine, 2-methyladenine, 3-methyladenine, and 8-methyladenine, J. Chem. Eng. Data 45 (2000) 626–629. V. Nikolaev, Vs nikolaev, zh. eksp. teor. fiz. 51, 1263 (1966)[sov. phys. jetp 24, 847 (1967)]., Sov. Phys. JETP 24 (1967) 847. J.R. Oppenheimer, On the quantum theory of the capture of electrons, Physical review 31 (1928) 349.