A calculation error resulted in all reported 800 nm probe pulse intensities is too low by a factor of 100.1 That is, the probe intensity range investigated is approximately 2 × 1012–2 × 1013 W cm−2 instead of 2 × 1010–2 × 1011 W cm−2. The reported probe intensities in the text should be multiplied by 100. Figures 4 and 10 should read as follows.
Amplitude coefficients for the parent molecular ion as a function of probe intensity in 4-NT (a) and 3-NT (b). Amplitude coefficients for the ion as a function of probe intensity in 4-NT (c) and 3-NT (d), respectively. Error bars denote 95% confidence intervals.
Amplitude coefficients for the parent molecular ion as a function of probe intensity in 4-NT (a) and 3-NT (b). Amplitude coefficients for the ion as a function of probe intensity in 4-NT (c) and 3-NT (d), respectively. Error bars denote 95% confidence intervals.
Transient ion signals of C7H7O+ in (a) 4-NT and (b) 3-NT at selected probe intensities (dots), indicated by different colors in the figure. Fit functions to Eq. (3) or a decaying exponential are shown as solid lines. The signals in 3-NT at intensities below 1013 W/cm2 were too noisy for curve fitting. The transient signal of the parent molecular ion is shown as the dotted line.
Transient ion signals of C7H7O+ in (a) 4-NT and (b) 3-NT at selected probe intensities (dots), indicated by different colors in the figure. Fit functions to Eq. (3) or a decaying exponential are shown as solid lines. The signals in 3-NT at intensities below 1013 W/cm2 were too noisy for curve fitting. The transient signal of the parent molecular ion is shown as the dotted line.
The error only affects the intensity of the probe pulse, not the pump (ionizing) pulse. The pump intensity was determined by measuring the Xe+ signal using established methods,2 while the probe intensity was determined from the energy, duration, and focal spot size, where a unit conversion error from the measured spot size caused the error in the probe intensity. Because the pump intensity was correctly reported, the conclusion that strong field adiabatic ionization of the parent molecules enables effective measurement of the ultrafast cation dynamics remains the same. The linear dependence of the transient ion signal amplitude coefficients with probe intensity also remains unchanged (Fig. 4), albeit with higher probe intensities. Thus, we suggest that the conclusion that a one-photon probe absorption results in C–NO2 cleavage may still be valid. However, the necessity of using high-intensity (∼1013 W cm−2) probe pulses to achieve a ∼50% reduction in parent ion yield suggests that the 800 nm probe wavelength is significantly detuned from the energy gap between the electronic ground state and excited state leading to NO2 loss. An alternative explanation for the linear dependence of the amplitude coefficients is that the probe electric field is sufficiently strong to modify the ground and excited state potential energy surfaces such that wavepacket excitation is enhanced in proportion to the degree of energy gap modification. This situation was found to be the case for halogenated methanes3 using similar probe electric field strengths (on the order of 109–1010 V/m) to our measurements. Thus, such strong-field dressed states may contribute in our measurements. Future experiments using different probe wavelengths and calculations of the ground and excited state potential energy surfaces will make it possible to assess the relative contributions of resonant absorption and strong-field dressed states in the C–NO2 bond cleavage mechanism.