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The presence of quasars at redshifts z > 6 indicates the existence ofsupermassive black holes (SMBHs) as massive as a few times 10^9 Msun,challenging models for SMBH formation. One pathway is through the directcollapse of gas in T_{vir} > 10^4 K halos; however, this requires thesuppression of H_2 cooling to prevent fragmentation. In this paper, we examinea proposed new mechanism for this suppression which relies on cold-modeaccretion flows leading to shocks at high densities (n > 10^4 cm^{-3}) andtemperatures (T > 10^4 K). In such gas, H_2 is efficiently collisionallydissociated. We use high-resolution numerical simulations to test this idea,demonstrating that such halos typically have lower temperature progenitors, inwhich cooling is efficient. Those halos do show filamentary flows; however, thegas shocks at or near the virial radius (at low densities), thus preventing theproposed collisional mechanism from operating. We do find that, if weartificially suppress H_2 formation with a high UV background, so as to allowgas in the halo center to enter the high-temperature, high-density "zone of noreturn", it will remain there even if the UV flux is turned off, collapsing tohigh density at high temperature. Due to computational limitations, wesimulated only three halos. However, we demonstrate, using Monte Carlocalculations of 10^6 halo merger histories, that a few rare halos couldassemble rapidly enough to avoid efficient H_2 cooling in all of theirprogenitor halos, provided that the UV background exceeds J_{21} ~ few atredshifts as high as z ~ 20.

H_2 Suppression with Shocking Inflows: Testing a Pathway for Supermassive Black Hole Formation