New measurements of Cabibbo-suppressed decays of D mesons with the CLEO-c detector

Using 281 pb(-1) of data collected with the CLEO-c detector, we report on first observations and measurements of Cabibbo-suppressed decays of D mesons in the following six decay modes: pi(+)pi(-)pi(0)pi(0), pi(+)pi(+)pi(-)pi(-)pi(0), pi(+)pi(0)pi(0), pi(+)pi(+)pi(-)pi(0), eta pi(0), and omega pi(+)pi(-). Improved branching fraction measurements in eight other multipion decay modes are also presented. The measured D ->pi pi rates allow us to extract the ratio of isospin amplitudes A(Delta I=3/2)/A(Delta I=1/2)=0.420 +/- 0.014(stat)+/- 0.016(syst) and the strong phase shift of delta(I)=(86.4 +/- 2.8 +/- 3.3)degrees, which is quite large and now more precisely determined.