@article{0f485e5521454190a8717c09ef1a0de8,

title = "Stark-assisted population control of coherent CS2 4f and 5p Rydberg wave packets studied by femtosecond time-resolved photoelectron spectroscopy",

abstract = "A two-color (3+ 1′) pump-probe scheme is employed to investigate Rydberg wave packet dynamics in carbon disulfide (C S2*). The state superpositions are created within the 4f and 5p Rydberg manifolds by three photons of the 400 nm pump pulse, and their temporal evolution is monitored with femtosecond time-resolved photoelectron spectroscopy using an 800 nm ionizing probe pulse. The coherent behavior of the non-stationary superpositions are observed through wavepacket revivals upon ionization to either the upper (12) or lower (32) spin-orbit components of C S2+. The results show clearly that the composition of the wavepacket can be efficiently controlled by the power density of the excitation pulse over a range from 500 GW cm2 to 10 TW cm2. The results are consistent with the anticipated ac-Stark shift for 400 nm light and demonstrate an effective method for population control in molecular systems. Moreover, it is shown that Rydberg wavepackets can be formed in C S2 with excitation power densities up to 10 TW cm2 without significant fragmentation. The exponential 1e population decay (T1) of specific excited Rydberg states are recovered by analysis of the coherent part of the signal. The dissociation lifetimes of these states are typically 1.5 ps. However, a region exhibiting a more rapid decay (≈800 fs) is observed for states residing in the energy range of 74 450-74 550 cm-1, suggestive of an enhanced surface crossing in this region.",

author = "Knappenberger, {Kenneth L.} and Lerch, {Eliza Beth W.} and Patrick Wen and Leone, {Stephen R.}",

note = "Funding Information: The authors gratefully acknowledge financial support by the Director, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and from the National Science Foundation, Chemistry Division Contract No. CHE-0452973, and Information Technology Research (ITR-0218731). Table I. Calculated and measured beat frequencies ( cm − 1 ) for superpositions of C S 2 * comprising 5 p and 4 f Rydberg states. The experimentally measured frequencies are in bold. The transitions that reveal the superpositions identified by TRPES are in the table heading. The uncertainty of the center frequency is included with the measured quantum beat. C S 2 n l 2 s + 1 [ Λ ] Ω u → C S 2 + Π 1 ∕ 2 2 4 f Δ u 1 4 f Π u 1 4 f ∑ u 1 5 p Δ u 1 5 p Π u 1 4 f Δ u 1 0 4 f Π u 1 70 ± 10 0 4 f ∑ u 1 295 ± 8 233 0 5 p Δ u 1 1811 1755 1522 0 5 p Π u 1 1952 1886 1653 115 ± 20 0 C S 2 n l 2 s + 1 [ Λ ] Ω u → C S 2 + Π 3 ∕ 2 2 4 f Δ 2 u 3 4 f Π u 3 4 f Δ u 3 4 f Δ 2 u 3 0 4 f Π u 3 306 ± 8 0 4 f Δ u 3 383 ± 11 77 0 Table II. Summary of pump-probe fitting results for C S 2 * determined from TRPES, including fitted lifetimes (in femtoseconds) and standard deviations for the exponential population ( T 1 and T 2 ) of the superposition states ( A : B , shown in the left column). The term ω 12 is the time between recurrences in femtoseconds. The corresponding beat frequency obtained from Fourier transformation of the time-domain data is presented in the right column in wave numbers. C S 2 n l 2 s + 1 [ Λ ] Ω u → C S 2 + Π 3 ∕ 2 2 T 1 T 2 ω 12 cm − 1 4 f Δ 2 u 3 : Π u 3 760 ± 10 1280 ± 40 101 ± 1 306 4 f Π u 3 : Δ u 3 1260 ± 30 1340 ± 30 85 ± 2 383 C S 2 n l 2 s + 1 [ Λ ] Ω u → C S 2 + Π 1 ∕ 2 2 T 1 T 2 ω 12 cm − 1 4 f Δ u 1 : Π u 1 1150 ± 40 850 ± 20 480 ± 10 70 4 f Δ u 1 : ∑ u 1 1150 ± 20 1610 ± 10 120 ± 10 295 5 p Δ u 1 : Π u 1 1630 ± 30 1160 ± 30 260 ± 20 115 FIG. 1. Energy level diagram of C S 2 showing the 4 f and 5 p Rydberg states accessed in the three-photon transition studied here. Only those levels that can be probed by one-photon wave packet interference are shown. The energies for the various orbital quantum numbers Λ of the 4 f and 5 p Rydberg states are taken from the spectral assignments of Refs. 20, 22, and 23 . The windowed area approximates the anticipated excitation region for resonant three-photon excitations with a 550 cm − 1 pump bandwidth. FIG. 2. (a) Energy level diagram for the 400 nm + 800 nm ( 3 + 1 ′ ) REMPI photoelectron scheme. Shown are the 4 f and 5 p Rydberg states that ionize to the C S 2 + Π 1 ∕ 2 2 and Π 3 ∕ 2 2 spin-orbit components. The upward vertical arrows represent the multiphoton excitation scheme and the downward vertical arrows correspond to the resultant electron kinetic energies. (b) Photoelectron peaks from the 400 nm pump + 800 nm probe region of electron kinetic energy distribution recorded with a pump power density of 600 GW ∕ cm 2 . (c) Pump-probe photoelectron peaks recorded with a pump power density of 10 TW ∕ cm 2 . Peaks arising from ionization to both the [ 1 ∕ 2 ] and [ 3 ∕ 2 ] spin-orbit components are distinguished under both excitation conditions. FIG. 3. Summary of time domain and frequency domain 400 nm + 800 nm ( 3 + 1 ′ ) REMPI photoelectron spectra. The photoelectron peaks arise from Rydberg intermediate states ionizing to the Π 1 ∕ 2 2 channel. The data are arranged by ascending excitation power density. The pump-probe traces presented in panel (a) are from the transient resonances populated by the 400 nm three-photon excitation with a power density of 600 GW ∕ cm 2 , while those in panel (b) are from levels populated with a power density of 5 TW ∕ cm 2 and those in panel (c) are populated with a power density of 10 TW ∕ cm 2 . The corresponding Fourier transformations are shown in Fig. 4 . The time and frequency-domain data clearly show that the Rydberg states that are resonant within the excitation window are sensitive to the pump power density, as explained in the text. FIG. 4. Fourier transformations obtained for superpositions ionizing to the Π 1 ∕ 2 2 channel are shown in the left column and those ionizing to the Π 3 ∕ 2 2 channel are shown in the right. Excitation power densities employed are (a) 600 GW ∕ cm 2 , (b) and (c) 5 TW ∕ cm 2 , and (d) and (e) 10 TW ∕ cm 2 . FIG. 5. Energy level diagram summarizing the beat frequencies observed from the wave packet analysis. Only relevant states are shown. FIG. 6. Time-domain signal arising from the C S 2 4 f Δ 2 u 3 → C S 2 + Π 3 ∕ 2 2 probe transition. The intermediate Rydberg level is prepared with 600 GW ∕ cm 2 excitation power density. The pump-probe trace is fitted to a decay of 760 ± 10 fs . FIG. 7. Temporal-domain response of the TRPES experiment. The residual raw data from integration of the C S 2 + Π 1 ∕ 2 2 channel as a function of pump( 400 nm pulse)-probe ( 800 nm pulse) delay are fitted to the model shown in Eq. (3) . The data shown here are recorded with a pump power density of 10 TW ∕ cm 2 . The fitting results for all superpositions observed are summarized in Table II . FIG. 8. (a) Dissociation lifetime of Rydberg states plotted as a function of orbital angular momentum ( Λ ) . The trend exhibits no dependence on Λ . (b) Dissociation lifetime plotted as a function of excitation energy. Most Rydberg states are fitted to exponential decays of approximately 1.5 ps ; however, those in the range between 74 450 and 74 550 cm − 1 decay more rapidly with lifetimes of approximately 800 fs . ",

year = "2007",

doi = "10.1063/1.2771165",

language = "English (US)",

volume = "127",

journal = "Journal of Chemical Physics",

issn = "0021-9606",

publisher = "American Institute of Physics Publising LLC",

number = "12",

}