  Collapse and fragmentation of uniform filamentary clouds under isotropic
far-ultraviolet external radiation are investigated. Especially, impact of
photodissociation of hydrogen molecules during collapse is investigated.
Dynamical and thermal evolution of collapsing filamentary clouds are calculated
by solving virial equation and energy equation with taking into accounts
non-equilibrium chemical reactions. It is found that thermal evolution is
hardly affected by the external radiation if the initial density is high ($n_0
> 10^2 \mathrm{cm^{-3}}$). On the other hand, if line mass of the filamentary
cloud is moderate and initial density is low ($n_0 \le 10^2 \mathrm{cm^{-3}}$),
thermal evolution of the filamentary cloud tends to be adiabatic owing to the
effect of the external dissociation radiation. In this case, collapse of the
filamentary cloud is suppressed and the filamentary cloud fragments into very
massive clouds ($\sim 10^{4-5} M_\odot$) in the early stage of collapse.
Analytic criterion for the filamentary clouds to fragment into such massive
clouds is discussed. We also investigate collapse and fragmentation of the
filamentary clouds with an improved model. This model can partly capture the
effect of run-away collapse. Also in this model, the filamentary clouds with
low initial density ($n_0 \le 10^2 \mathrm{cm^{-3}}$) fragment into massive
clouds ($\sim 10^4 M_\odot$) owing to the effect of the external radiation.
