CL600 Captain reports track deviation departing LAS Runway 19R on SHEAD5 RNAV. When Captain calls for NAV selection; pilot not flying inadvertently selects HDG causing right turn. Wake turbulence from aircraft departing Runway 25R is encountered at this time; delaying recognition of the inappropriate turn.

Narrative

I was pilot flying; LAS; was departing Runways 01L/R. Clearance was 'turn left heading 240 degrees for radar vectors to the SHEAD5 departure; maintain 7000 FT.' (Unrelated to this report filing; I feel this is a poor clearance; and that some point on the departure should be specified. Granted however; a 240 heading will eventually take you across one of the procedural tracks in the departure.) Departure was briefed with pilot monitoring/pilot not flying prior to passenger arrival with emphasis that it was to be a 'heading' (pilot navigation) departure initially; not the charted SHEAD5 departure with an FMS lateral mode selection of [NAV]; nor a first fix off of the DER; etc. After loading passengers and starting engines we heard ground control giving revised departure procedures to other aircraft due to a flow change to Runway 19L/R departures; I re-selected the SHEAD5 departure in the FMS and [EXEC](executed) it; but left the runway selection open; as you are sometimes cleared to the parallel runway for takeoff. The possible first intersections are JAKER (Runway 19R) and FIXIX (Runway 19L). During taxi to Runway 19R I briefed that it was now the full SHEAD5 departure; a 'NAV' (FMS lateral mode selection) departure; with possible first fixes of JAKER or FIXIX; depending on runway. We did not realign the heading knob from the previously selected 240 degree heading. When we were cleared for takeoff from Runway 19R I selected Runway 19R in the FMS; [EXEC] (executed) it; and verified the first fix as JAKER in both the FMS and on the paper chart. After takeoff I directed the pilot monitoring/pilot not flying to 'Select [NAV]; [FLC]; Speed 200; [VNAV].' I did not see that the pilot monitoring/pilot not flying instead selected [HDG]; [FLC]; 200. While over the departure end of Runways 19R/25L/R we encountered pronounced turbulence with some rolling moment which I assumed was possible wake turbulence from departing traffic from Runway 25L/R. Simultaneously the FD command bars were indicating a turn to the right to intercept what I thought was the outbound course but was in reality a right turn to heading 240. I realized quickly that the angle between my (still turning) heading was too great for the proximity to the course and that the course needle was rapidly closing; then crossing under the aircraft. I immediately rolled the aircraft to the left and selected [NAV] to re-initiate the course intercept. At that time ATC (I don't know if it was Tower or Departure) cleared us to 'Turn left heading 190 (an approximation of the outbound course); which I selected and engaged [HDG]. I was not aware of a frequency change but heard Departure issuing clearances; I asked the pilot monitoring/pilot not flying to check in with Departure but she stated that we had not been handed off by Tower yet. I asked her to report level at 7000 FT on that frequency; up on which Departure subsequently cleared us to the remaining segments of the departure procedure. I attribute the deviation to my failure to understand that the pilot monitoring/pilot not flying did not fully understand the change in the departure clearance and how it was to be flown (though I specifically referred to the change twice); my not selecting a more useful value under the heading bug prior to takeoff (ie.; runway heading); and failing to notice the incorrect flight director selection that was made after takeoff; during the time we were encountering the turbulence. Contributing factors for the pilot monitoring/pilot not flying were the law of primacy (the first departure that was briefed was 'selected' on the FD) and the law of repetition most departures are pilot nav; so most FD selections after most takeoffs are '[HDG]; [FLC]; Speed 200; etc.)' pilot monitoring/pilot not flying is rated and experienced in type; also with over 2000 hours in type; and over 5000 hours TT. I understand this SID is problematic for ATC with respect to proper aircrew compliance; had briefed that aspect;and had verified the first fix appropriate to the runway of takeoff; though local ATC does no longer require that to be read back as they used too.