Ionization of alkanes to form radical cations activates their otherwise unreactive C-H bonds, facilitating important chemical processes such as hydrocarbon cracking. This work investigates the radical cation dissociation dynamics of hexane (C₆H₁₄) structural isomers by using femtosecond time-resolved mass spectrometry and quantum chemical calculations. All five isomers exhibit competition between the yields of fragment ions arising from direct C-C bond cleavage or dissociative rearrangement with hydrogen migration on dynamical time scales of ∼50-300 fs, suggesting that hydrogen migration in the metastable cations operates on such short time scales. Additional isomer- and conformer-specific dynamics are observed. Preferential dissociation pathways in the branched isomers are found to arise from geometric relaxation to cation structures with one elongated C-C bond. Coherent vibrational excitation along this elongated C-C bond in 3-methylpentane and 2,3-dimethylbutane results in ion yield oscillations in the first ∼300-400 fs after ionization. Enhanced depletion of the molecular ion signal in <i>n</i>-hexane compared to that in the branched isomers is attributed to a strongly coupled excited state in the most populated conformer that can be accessed by a two-photon transition. Collectively, these results provide a foundational understanding of dissociation dynamics in alkane radical cations and how these dynamics are affected by specific isomer and conformer structures. All five isomers exhibit competition between the yields of fragment ions arising from direct C–C bond cleavage or dissociative rearrangement with hydrogen migration on dynamical time scales of ∼50–300 fs, suggesting that hydrogen migration in the metastable cations operates on such short time scales. Additional isomer- and conformer-specific dynamics are observed. Preferential dissociation pathways in the branched isomers are found to arise from geometric relaxation to cation structures with one elongated C–C bond. Coherent vibrational excitation along this elongated C–C bond in 3-methylpentane and 2,3-dimethylbutane results in ion yield oscillations in the first ∼300–400 fs after ionization. Enhanced depletion of the molecular ion signal in n -hexane compared to that in the branched isomers is attributed to a strongly coupled excited state in the most populated conformer that can be accessed by a two-photon transition. Collectively, these results provide a foundational understanding of dissociation dynamics in alkane radical cations and how these dynamics are Previous studies on multiple classes of polyatomic molecules have shown that the presence of electronic excited states in the cation, with energies lower than the ionizing laser photon, tends to result in extensive fragmentation during SFI, while the absence of low-lying and strongly coupled excited states enhances the yield of intact molecular ions. In contrast, the dominant n -hexane conformer 1 (90% at the D 0 geometry) has extremely strong coupling ( f = 0.28) to an excited state 2.6 eV above the ground state, which could be reached by two-photon excitation with a 1.74 eV probe pulse. Because the relatively high intensity of the probe pulse (∼10 13 W cm –2 ) is expected to enable two-photon excitation, enhanced n -hexane fragmentation compared to the branched isomers may be expected at long pump–probe delays. Figure shows the transient C 6 H 14 + molecular ion signals for each isomer. In 3-methylpentane, the oscillations of the molecular ion (dark red) and C 4 H 8 + (yellow) can be seen to be roughly in-phase with each other and roughly out of phase with the C 4 H 9 + signal (dark orange). Similarly, the oscillations in the molecular ion (dark red) and C 3 H 6 + (green) signals from 2,3-dimethylbutane are roughly in phase with each other and out of phase with the C 3 H 7 + (yellow-green) signal. The antiphase oscillations between pairs of fragment ions indicate that the dissociation pathways leading to fragmentation of 3-methylpentane into C 4 H 8 + or C 4 H 9 + and fragmentation of 2,3-dimethylbutane into C 3 H 6 + and C 3 H 7 + are in direct competition. ,, Specifically, this result suggests that absorption of a photon from the probe pulse at a specific point along the potential energy surface can cause metastable 3-methylpentane ions that would spontaneously form C 4 H 8 + to instead produce C 4 H 9 + . Similarly, metastable 2,3-dimethylbutane ions that would spontaneously form C 3 H 6 + instead produce C 3 H 7 + . This competition between formation of C 4 H 8 + or C 3 H 6 + , which involve hydrogen migration, and the direct C–C cleavage products C 4 H 9 + or C 3 H 7 + suggests that electronic excitation of metastable C 6 H 14 + cations can selectively suppress spontaneous dissociation pathways involving migration of one hydrogen atom. Overall, the competition between C 2 H 5 + and C 2 H 3 + in n -hexane and 3-methylpentane at short pump–probe delays resembles the competition among C 3 H 5 + and C 3 H 3 + fragments seen in Figure b, suggesting similar short time scales for dissociation pathways to C 2 H 3 + involving the loss of two hydrogen atoms. To quantify the dynamical time scales seen in Figures through , all transient ion signals were fit to exponential decay functions convoluted with the Gaussian instrument response function, following the literature method. The longer T 2 time constant could be associated with an initial or sequential bond cleavage step. However, we note that further computational work, including molecular dynamics simulations, would be needed to support the assignment of any experimental time constant to a specific reaction process. Even without such computations, visualization of the complex ion yield dynamics from the large numbers of fragments observed in the hexane isomers can be aided by calculating the Pearson correlation coefficient for each pair of ions over a specific range of pump–probe delays.