Time-resolved high-harmonic spectroscopy of the photodissociation of CH₃I and CF₃I

Abstract

The photodissociation dynamics of iodomethane (CH 3 I) and trifluoroiodomethane (CF 3 I) have been studied using time-resolved high-harmonic spectroscopy. The molecules were photoexcited in a transient grating geometry to their respective A bands by laser pulses centered at 267 nm and were probed through high-harmonic generation driven by a delayed 800 nm laser pulse. Both molecules display a fast buildup of the diffracted high harmonics (H9-H15) followed by a slower decay, while the undiffracted harmonics exhibit an opposite modulation. The time scales on which the signals reach their asymptotic values were found to be slower in CF 3 I compared to CH 3 I and to weakly increase with high-harmonic order in both molecules. In the case of CH 3 I the obtained time scales are in agreement with dissociation times measured by other techniques. Our results on CF 3 I constitute the first time-resolved measurements of the A-band dissociation. A simple theoretical model for the variation of the harmonic phase induced by the changing vertical ionisation potential is combined with one-dimensional nuclear wave packet propagation and shown to qualitatively account for the main observations.

Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates

“…(1) and (2), the energy resolution of a ZP monochromator is determined by the values of β , d, and ∆x . Equation (1) indicates that the value of d sin β is constant for a defined geometry of the HHG setup and a particular energy resolution E/∆E desired in an experiment. A calculation procedure of the optimal structure period d is presented in [27].…”

“…Short light pulses in the extreme ultraviolet (XUV) range find a wide variety of applications in studies on electronic and structural dynamics of molecules and molecular complexes [1][2][3]. In particular, photoelectron spectroscopy with the use of XUV radiation is a powerful method to probe the electron density in a valence shell of a molecular system.…”

Probing Electronic Dynamics during Photochemical Reactions

“…[13,15,16,18] While the interference between high-harmonic emissions of excited and unexcited molecules is exploited in both cases, the transient-grating configuration, illustrated in Fig. 1, provides the intensity of the diffracted radiation as an additional observable that complements the intensity of the undiffracted radiation.…”

“…[9][10][11][12] The application of high-harmonic spectroscopy to studying photochemical dynamics, termed time-resolved high-harmonic spectroscopy (TRHHS), has been described in refs. [13][14][15][16][17][18] and will be reviewed here. So far, TRHHS has been applied to studying the photodissociation of Br 2 , [13,14,17] the conical intersection dynamics and subsequent dissociation of NO 2 , [15][16][17] both following photoexcitation at 400 nm, as well as the non-adiabatic photodissociation of CH 3 I and CF 3 I following photoexcitation at 267 nm.…”

“…So far, TRHHS has been applied to studying the photodissociation of Br 2 , [13,14,17] the conical intersection dynamics and subsequent dissociation of NO 2 , [15][16][17] both following photoexcitation at 400 nm, as well as the non-adiabatic photodissociation of CH 3 I and CF 3 I following photoexcitation at 267 nm. [18] Theoretical models of increasing detail have also been developed and are described in refs. [14,16,17].…”